Riku is five years old during Kingdom Hearts Birth by Sleep, fifteen during the events of Kingdom Hearts and Kingdom Hearts: Chain of Memories, and sixteen during the events of Kingdom Hearts 358/2 Days, Kingdom Hearts II and Kingdom Hearts 3D: Dream Drop Distance. Riku's name is derived from the Japanese word for "Land".
 Kingdom Hearts Birth by Sleep
When Terra visits Destiny Islands, he can already sense Riku's potential, and asks why Riku wants to leave his island. Riku tells Terra that someone else left the island long ago, and visited other worlds. Riku states that he would like to leave his world too in order to become strong enough to protect his friends and everything he holds dear. During their conversation, Terra sees a vision of a white-haired man who then transforms into Riku's sixteen-year-old self. This convinces him to choose Riku as his successor, and lets Riku hold his Keyblade to test his strength. He convinces Riku to keep their conversation a secret to preserve the world order.
He and Sora later encounter Aqua, who finds their friendship similar to that of hers, Terra's and Ven's, and asks Sora to protect Riku if he ever loses his path.
Some time afterwards, Riku and Sora are resting on a beach under a starry night. When they are ready to go home, Riku sees Sora's sudden look of sadness and says that perhaps someone from another world is feeling sad somewhere and suggests that Sora try and reach out to him. After Sora reaches out to Ventus, they both look up at the starry sky.
 Between Kingdom Hearts Birth by Sleep and Kingdom Hearts
One night, there is a meteor shower and a mysterious girl appears on the islands from another, far off world. Riku, Sora, and Kairi quickly forge a powerful friendship. Soon after Kairi's arrival, Riku and Sora go to the secret place, a small cave that they frequently explored. While there, the two spot a mysterious door, though neither one can find a way to open it. The two decide to leave, but Riku manages to get a glimpse of Destiny Islands' Keyhole.
 Kingdom Hearts
Riku, Sora, and Kairi live on the Destiny Islands. The three construct a raft and gather supplies so that they can set out and search for other worlds. He and Sora continue their rivalry, and Riku takes jabs at Sora over their relationship with Kairi, telling him that if Sora does not share a paopu fruit with Kairi soon, he will.
On the night before their journey. Riku opens the door in the secret place and the Heartless invade the islands. Kairi and Sora each set out for the island to make sure their raft is safe. Sora finds Riku, but finds that Riku is only eager to escape the islands. Darkness surrounds the two, and Riku disappears into it, while Sora gains the Keyblade.
In exchange for Riku's cooperation in gathering the Princesses of Heart, she agrees to find Kairi and bring her to him. During this time, Riku comes to possess a blade called Soul Eater. Riku comes across Sora in Traverse Town. He takes possession of Sora's Keyblade for a few moments before giving it back to Sora, much to Sora's surprise, and then he suddenly leaves. Watching Sora from a distance, Maleficent turns Riku against Sora, telling him that Sora has abandoned him and Kairi for traveling with Donald Duck and Goofy. However, he is still highly suspicious of her motives.
During Sora and Aladdin's fight with Jafar in Agrabah, Riku takes Jasmine to Hollow Bastion under Maleficent's orders. Maleficent reveals the whereabouts of Kairi's body. She claims that the only way to save Kairi, who appears to have lost her heart to the darkness, is to gain access to Kingdom Hearts.
Riku meets Sora again in Monstro, intending to use Pinocchio to help him find a way to save Kairi's heart. However, Pinocchio is captured by the Parasite Cage, and Riku works together with Sora, Donald, and Goofy to save him. Afterwards, Riku kidnaps Pinocchio, and is pursued by Sora, Donald, and Goofy into Monstro's stomach. Riku asks Sora to join him and help him rescue Kairi, but Sora refuses, knowing that Riku's methods are wrong. When the Parasite Cage returns, Riku vanishes into a Corridor of Darkness.
Maleficent bestows the power of darkness on Riku, giving him the power to command the Heartless. He then goes to Neverland, traveling on Captain Hook's ship, where Kairi's body is being kept. He appears before Sora, showing him Kairi's body. Sora warns Riku that the Heartless will eventually turn on him and devour his heart, but Riku refuses to listen and retreats after using his new powers to summon AntiSora. However, before he heads back to Hollow Bastion, he tells Captain Hook that the captured Wendy is not a Princess of Heart. Riku takes Kairi and recklessly returns to Maleficent's castle via the Corridors of Darkness without a vessel, putting a strain on his heart. While he is drained from the trip, Maleficent unlocks the last of Riku's dark power.
At Hollow Bastion, Sora again meets Riku, stopping him from taking down the wounded Beast. Riku then forcibly summons the Keyblade away from Sora, telling him that he was "just the delivery boy" and that Riku is the true Keyblade master. After leaving Sora with the toy sword he used on Destiny Islands, he departs, and Donald and Goofy reluctantly follow him as per The King's orders.
Sora makes his way to the foyer of the castle, with the help of Beast. Riku, taking on a new appearance with the increasing strength of his dark powers, tells him to quit, but Sora refuses to leave without Kairi. Riku, intending to prove to Sora that he is the strongest of the two, attacks his old friend, but Donald and Goofy go to Sora's aid, finding themselves unable to betray Sora after all that they had been through together. With the strength of his friends, Sora reclaims the Keyblade, and drives Riku to fight him.
Riku, defeated, manages to escape, but he is confused as to why Sora was able to regain the Keyblade. A cloaked figure appears to him from the Darkness, telling him that only one with a stronger heart can claim the Keyblade, and Riku's was weaker than Sora. However, the figure tells him that plunging himself into darkness will make his heart stronger. Riku does so, and his is possessed by the dark figure.
The possessed Riku then comes before Maleficent, and warns her of the dangers of unlocking the Final Keyhole. When she claims not to be afraid, Riku shows a new, dark Keyblade created with six of the seven princesses' hearts. However, it doesn't react to the Keyhole. Realizing it is still needing Kairi's heart to be complete, Maleficent heads off to handle Sora and company. After Maleficent is defeated by Sora, Riku appears with his Keyblade and explains that unlike Sora's Keyblade, this Keyblade possesses the ability to unlock a person's heart, and Riku demonstrates this by piercing Maleficent's chest, allowing the immense darkness that is attracted to her to overtake her heart, transforming her into a giant dragon. When Maleficent is defeated again, he reappears, commenting on how Maleficent was being used by the Heartless before disappearing again.
Riku, declaring himself to be Ansem, the Seeker of Darkness, confronts Sora in the Grand Hall and reveals that Sora has Kairi's heart in his body. While Donald and Goofy look on, Riku and Sora clash again, with Ansem's presence amplifying Riku's dark powers. He fades away when he is defeated, but after Sora impales himself with the Keyblade to release Kairi's heart and disappears, Ansem reveals himself and attacks Kairi, Donald, and Goofy. Riku uses the last of his strength to hold back his possessor, and yells to the others to run. After they leave, Riku and Ansem are pulled into the darkness coming from the Final Keyhole.
A newly restored Sora, along with Donald and Goofy, eventually make their way to the End of the World. There, in the remnants of Destiny Islands, they once again confront Ansem, who has full control of Riku, and defeat him after a series of battles at the Door to Darkness.
Riku is restored after Ansem's defeat, and he appears on the other side of the Door to Darkness, aiding Sora in closing it, although unable to cross it himself. Waiting to enter the Realm of Light are thousands upon thousands of Heartless, which only causes further problems for the two friends. However, King Mickey wards them off with his Keyblade. The King and Sora then proceed to close and lock the door from either side, and Riku is stuck in the Realm of Darkness with the King, but not before he tells Sora to take care of Kairi.
 Kingdom Hearts: Chain of Memories
Riku awakes in the lowest basement of Castle Oblivion, being led there by his heart resonating with Sora, who also happens to be in Castle Oblivion, though on the ground floor. A dark card and a disembodied voice present themselves. The Voice offers Riku the chance to sleep and forget his troubles as well as the light, or take the card and take the first steps toward the truth. Riku takes the card confidently stating that "This looks like a boring place to take a nap anyway."
Riku arrives in none other than Hollow Bastion, though only a version of it crafted from his memories. However, though Hollow Bastion is the same as he remembered it, he is unable to find anyone. All the while he searches, the voice speaks to and mocks the young teenager.
At long last, Riku meets someone: Maleficent. Maleficent taunts him and his refusal of the darkness, but Riku fights and defeats her, hoping to prove that he is above the darkness.
Riku leaves Hollow Bastion, only to see the true form of Castle Oblivion. The voice again comes to Riku, but this time reveals himself to be Ansem, who wants to take over Riku again. However, though Ansem is powerful, King Mickey comes to aid Riku with his light. Riku then manages to fend off Ansem for the time being. But before he leaves, the Heartless leaves Riku with some world cards and the ability to wield his inner darkness as a weapon.
Riku soon realizes that he has the power to detect the "smell" of darkness, and is discouraged by it, though King Mickey comforts him. However, King Mickey can only appear to Riku as a projection, for he is still in the Realm of Darkness. Still, with King Mickey's encouragement, Riku ascends the basements of Castle Oblivion in order to rid himself of his darkness. Meanwhile, as Riku travels through the lower levels of Castle Oblivion, Sora ascends the upper floors, being manipulated by Marluxia, a member of the mysterious Organization XIII and the lord of Castle Oblivion. But three other Organization members, Vexen, Lexaeus, and Zexion work to counter Marluxia by using the dark-wielding Riku against the light-wielding Sora.
To further the trio's goals, Vexen independently appears before Riku and the latter wonders if Vexen is with "Ansem" (Xehanort's Heartless). Vexen cryptically responds that he is with "another Ansem". Still, Riku fights against Vexen, seeing him as an enemy. However, the battle only helps Vexen, who uses the data he gathered from the battle to create a replica of Riku. The replica soon comes to battle Riku, mocking Riku's fear of the darkness while the replica embraces it. However, the real Riku proves victorious, and the replica runs off.
Soon, Ansem, Seeker of Darkness, appears again, saying that the replica is a model of what Riku should be. But Riku only reaffirms his desire to conquer his darkness.
Passing through much of the castle (by this time, the bulk of Sora's adventure is complete, and Larxene and Vexen have been eliminated) Riku finds Lexaeus. Lexaeus, like the others, tells him that he should accept the darkness again, because if he doesn't, his journey will end here. The two fight, and Riku only manages to wear him down. As Riku moves in for the finishing blow, Lexaeus summons his herculean strength and knocks Riku unconscious with his Axe Sword. Lexaeus decides to eliminate him since taking him down was too much trouble, but as he does, he notices Riku becoming possessed by Ansem, Seeker of Darkness. This catches Lexaeus off-guard, and the possessed Riku takes the opportunity to put an end him. Although Lexaeus is defeated, Riku ends up having a struggle with Ansem that he nearly loses. Just before the dark being can overwhelm Riku, Mickey saves him again and manages to bring him out of the darkness.
Riku comes closer to the ground level, just as Marluxia's scheme fails and Sora finishes him off. Riku senses Marluxia's defeat, and Zexion quickly arrives on the scene to explain it. But he also reveals that Sora is the one who did the deed, much to Riku's surprise. Zexion quickly asks if Riku is capable of seeing Sora, for Riku shouldered the darkness for so long, and Ansem still resides in his heart. Riku tries to resist Zexion's comments, but Zexion ultimately gives him a world card of Destiny Islands.
In Destiny Islands, Riku meets all of his friends, but they are all silent and they eventually disappear, even Kairi. Zexion throws all of Riku's fears at him at once, telling him he's responsible for causing them to disappear, and that he belongs to the darkness now. He finally transforms an illusion of him into a Darkside Heartless, telling him this is what he has become. Riku defeats the Heartless as Zexion disguises himself as Sora. He tells him that it's finally time to face the light.
Riku sinks into the light as he begins to fade, but Naminé appears in the form of Kairi and tells him that he can't fade, because light can't destroy him, and neither can darkness, so he should accept both to drive away his fears. He awakens his dark powers again, admitting that it's a part of him and not evil, defeating Zexion. Zexion disappears, but is quickly eliminated by the Riku Replica with Axel.
Riku nearly makes it to the main floor as Ansem, Seeker of Darkness, appears to control him, but King Mickey defends Riku again and finally appears for real. Riku is relieved at finally having a real friend with him. King Mickey explains that he found a card which showed him Riku's heart and he followed it back to him. Riku uses the card, and ends up in Twilight Town. Ansem, Seeker of Darkness, appears again, but Riku tells him that he's not "Ansem", because his scent is not darkness—but rather something else. Riku also sees that this man is the voice that presented itself at the beginning of his journey. The voice finally appears and introduces himself as DiZ. Riku asks him what he really wants from him, and DiZ tells him he wants him to choose between Light and Darkness, because he lies in-between. The decision will be decided with Naminé, whom Riku looks for.
However, the Riku Replica manages to find him, and demands another fight to prove him "worthy". The replica intends to destroy Riku in order to become real, but fails. However, Riku comforts him by saying that the replica's heart will go to the same place as the real one's, before the replica vanishes out of existence.
Riku meets up with Naminé, who is with Sora in his memory pod, and explains the situation. She offers to seal away Ansem and Riku's darkness, so that he may forget them, but will have to sleep to do so. Riku refuses, hoping to win on his own, and leaves a satisfied Naminé. However, before he departs, he tells Naminé that he knows that it was she who appeared to him as Kairi, commenting that they smell the same.
After meeting Naminé, DiZ appears again to Riku and the King (who notes that DiZ seems familiar). Knowing his choice, DiZ gives Riku a card that will draw out Ansem, Seeker of Darkness. After DiZ leaves, Riku tells King Mickey to destroy him if he fails to stop Ansem, but the King refuses, saying he'll only help him regain control, and never harm him. Riku concedes.
Riku faces Ansem alone for one final battle. Ansem asks why he still refuses him if he accepts darkness now, and inquires if Riku is still scared of the darkness. Riku denies this and merely says, "I just can't stand your foul stench." They fight and the last of Ansem is destroyed, but not before he says a part of him is still in Riku, and that he shall return.
Riku and Mickey wait at the crossroads. Riku tells him that he can't go home yet, as "Ansem's" shadow still lingers in him, but Mickey says the darkness is a part of him. Darkness is not all bad, because Riku has chosen a road he never thought of before, one of both Light and Darkness. Riku, who now forms an equally strong bond to the King as Sora's friendship to Donald and Goofy, calls Mickey by his name at the King's request.
They leave, taking Organization coats that DiZ gave them prior to confronting Ansem, and DiZ appears for one final question: if he shall take the "road to light" or the "road to darkness". Riku chooses neither; he instead chooses to take the middle road, "The road to dawn". Riku and King Mickey eventually make it out of the plains and separate after Riku realized he couldn't completely rid himself of the darkness festering in him. Deciding to return to DiZ and offer his help, Riku dons a blindfold, so that "his eyes couldn't lie" about the darkness that he is preparing to use.
 Kingdom Hearts 358/2 Days
Sometime after these events, Riku encounters Xion on the bridge in Beast's Castle. As she lies defeated, Riku pulls off her hood and pulls up his blindfold to get a good look at her. He is shocked by her appearance. Riku interrogates her as to her identity and use of the Keyblade, while Xion demands to know why he's dressed as a member of the Organization. When Riku calls Xion's Keyblade a sham, she angrily reacts but is slapped down, with Riku advising her to leave the faithless Organization, while denigrating himself for his own mistakes in accepting the darkness.
Soon after, Xion leaves the Organization and joins up with Riku. He takes her to Destiny Islands, where her confused memories give her an intense nightmare shared with Roxas involving Zexion and Riku's battle at Castle Oblivion's facsimile of Destiny Islands. While comforting her, Riku recalls a prior conversation with Naminé discussing what he needs to do to awaken Sora. After Xion wakes up on Destiny Islands, she inquires about Sora and the "girl he's always with", to which Riku explains that the girl is Kairi, a special friend of Sora's, and that the reason Sora is unable to wake up is that some of his memories are held within Xion. Despite needing Xion to reunite with Roxas and Sora, Riku gives her time to decide what she wants to do, with the advice that she should choose what is best for everyone.
After some time, Xion leaves with Riku to stay at DiZ's base in Castle Oblivion. Roxas and Axel continue to search for her across the worlds, and finally make contact in Twilight Town, but Xion quickly takes her leave while Riku stays behind to distract them.
Later, Riku and DiZ check up on Sora's progress, and DiZ commands that Riku finally act to resolve the Xion situation. In The Woods, King Mickey runs across Riku-Ansem and prepares to attack, supposing him to be Xehanort's Heartless, but calms himself when Riku replaces his blindfold and returns to his normal form. Riku informs the king that he is leaving to fight a member of the Organization, and demands Mickey to protect Sora in the event that he does not return.
Sure enough, Riku runs into Roxas at Memory's Skyscraper as the latter begins a rampage to free Kingdom Hearts. After fending off several Neoshadows, Roxas spots Riku and attacks, but a failed Strike Raid puts his Oblivion in Riku's hands. Riku and Roxas are both jolted by the fading memories it communicates of a now-erased Xion, and bemusedly finish off the remaining Neoshadows before turning on each other.
Demanding to know why Riku stands in his way, Roxas explains that he is seeking to retrieve his lost friend by freeing Kingdom Hearts, but is angered when Riku responds that Xion's memories are already too far gone to save her. A furious Roxas is initially able to gain the upper hand, but is knocked down just when victory seems in sight. Riku returns the Oblivion to the unconscious Roxas and prepares to transport him, but is surprised when Roxas revives and once again attacks; in response, Riku jostles his sleeping memories by taunting Roxas as he once did Sora, inducing Roxas to respond as Sora would and confirming Riku's suspicions of Roxas: that he is Sora's Nobody. Even more enraged, Roxas slashes at Riku with the Oblivion and it passes on one final memory of Xion, which implore Riku to save Roxas by stopping him. Left with no other choice, Riku releases the darkness imprisoned in his heart and once again takes on Ansem's form, this time permanently. realizes that if he is to win in the Realm of Darkness, he must submerse himself in the same darkness. He quickly dispatches Roxas, then returns him to DiZ's base at the Old Mansion, where he introduces himself as "Ansem".
 Kingdom Hearts II
Riku continues to ally himself with DiZ, as they have a common goal: to help Sora awaken (though Riku finds his memories of Sora fading, being a side-effect of Naminé's toying with Sora's memories). Roxas's memory is erased by DiZ and he is placed into a Simulated Twilight Town, to live out his days until the time comes for him to meet Sora. Meanwhile, Riku watches over Roxas, periodically entering the town in order to keep Roxas ignorant to the truth, including keeping Naminé from saying anything important to Roxas. He also takes some keepsakes of Roxas's during some of his visits. With all these deeds done, Riku finally demands to know what DiZ's true objective is. Upon hearing that it is merely revenge (DiZ does not disclose against whom it is), Riku clenches his fist, shocked and disgusted at how DiZ is merely using him and Sora for his own selfish reasons.
Eventually, when the time comes for Roxas, Riku makes sure to prevent the Nobodies from flooding the town. Soon, the goal Riku had been searching for is finally reached: Roxas joins with Sora. Though DiZ orders him to eliminate Naminé, Riku desires no part in DiZ's prejudice revenge and hands her to the now-renegade Axel of Organization XIII before leaving DiZ.
Riku, after Roxas joins with Sora, comes into contact with King Mickey. Riku begs King Mickey not to reveal his whereabouts and condition to Sora, and the King reluctantly agrees. He then leaves the King the digital versions of Olette's Munny Pouch and Roxas's crystal orb that he had pilfered from Roxas earlier.
Later, Axel tries to kidnap Kairi in an attempt to use her to turn Sora into a Heartless so Roxas would be reborn. However, Riku rescues Kairi by opening a Corridor of Darkness, and takes her to Twilight Town, where she meets Hayner, Pence, and Olette, but never reveals his identity. However, Axel again appears and kidnaps Kairi, but another member of Organization XIII, Saïx, manages to take Kairi away from Axel, with the intent to use her to fuel Sora's rage. At the battle for Hollow Bastion, Sora, Donald, and Goofy end up in an empty realm, where Riku arrives. He says nothing to them, and only leaves the trio a box that contains sea-salt ice cream and a picture of Roxas, Hayner, Pence, and Olette in front of the haunted mansion before immediately departing.
Riku also arrives at The Land of Dragons, trying to warn the Emperor of a Heartless dragon that Xigbar created. But he ends up meeting Sora, and Sora attacks him, thinking Riku to be an Organization member. However, Sora sees that Riku is wielding the Soul Eater, and begins to suspect Riku's identity. But Riku still goes ahead with his mission, and warns the Emperor (but had to defeat Li Shang in order to do so). When Sora talks to the Emperor, the wise ruler's description of the man further cemented Sora's idea that the man he fought was Riku; though unaware of why he is wearing the coat, Sora is nonetheless relieved to know that Riku is safe.
Riku later appears in the World That Never Was, after Naminé rescues Kairi. The two are faced against Saїx, but Riku quickly comes to the rescue, his Soul Eater having now transformed into a Keyblade called Way to the Dawn. To Kairi's surprise, Naminé calls Riku by name, and disappears. Though Riku attempts to depart when Saїx escapes, he is stopped by Kairi and Pluto. Kairi, excited to see Riku, removes his hood, but is met with the face of Ansem, Seeker of Darkness. She takes it in stride, seeing the true Riku underneath his current form.
Kairi later is attacked by Heartless in her attempt to help Sora, and saved by Riku. He then gives Kairi the Destiny's Embrace Keyblade so that she may fight. After Sora defeats Xigbar, he and Kairi reunite. Riku tries to take his leave, but Kairi stops him. She then reveals Riku's identity, and with some concentration, Sora also sees Riku underneath his dark appearance. The revelation makes Sora overjoyed to the point of tears. Riku explains that he did not want to be found, thanks to his appearance, and confirms Sora's suspicions of the clues they found- namely, the ice cream and Roxas' photo. Still, he and the others make their way up the castle, defeating the remaining Organization members save for Xemnas. During this time, Riku reveals the truth about Roxas to Sora, and realizes that he never had to fight him; Roxas had left Organization XIII because he had wanted to meet Sora in the first place, and would most likely have met him either way over time.
Near the top, Riku reunites with King Mickey and DiZ, his true name being Ansem the Wise, who is using a machine to try and encode Kingdom Hearts into data. Xemnas also arrives, and he and Ansem the Wise trade bitter words. The machine then explodes, unable to handle Kingdom Hearts, sending Ansem the Wise to the Realm of Darkness while causing countless hearts Xemnas had collected into Kingdom Hearts to rain down on the world, creating a slew of Heartless. The explosion also cleanses Riku's heart and restores Riku to his original form, though he is still remorseful. After some encouragement, Riku transcends the rest of the castle, abandoning his cloak and blindfold. He and the others also encounter Maleficent and Pete, who decide to hold off the hordes of Heartless that are overtaking the castle, but only so that they will eventually take the castle for their own.
Riku and the others then confront Xemnas, refusing his demand to gather more hearts. Xemnas then removes Sora from the area, fighting him one on one, with everyone else calling out to him. When Sora returns, they see that Xemnas has already reached Kingdom Hearts, and disappears into it. A door, constructed by the will of the worlds, appears, and the three wielders of the Keyblade open it up and follow Xemnas. After a tough battle, Naminé appears again, opening up a corridor of darkness that leads to Destiny Islands, as Riku can no longer use them. However, Xemnas attacks, riding on a gigantic robotic dragon, and separates Sora and Riku from the others. After a series of battles, the two of them are drawn into nothingness by Xemnas and face in a final, exhausting battle.
Towards the end after the final attack used by Xemnas, Sora is left open and Riku takes a blow intended to finish off his friend, which allows Sora to finish Xemnas off with both Riku and Sora firing a beam of light from Sora's Keyblade. After the fall of Xemnas, Sora and the injured Riku face an onslaught of Dusks ready to fulfill their master's final order: eliminate the Keyblade wielders. However, the Dusks disintegrate back into nothingness, and Sora and Riku escape the realm, entering the Dark Meridian.
Having the time to finally talk, the two reconcile with each other. Riku then comes across a letter in a bottle, written by Kairi, and gives it to Sora, believing him to be the proper recipient. Sora then manages to open the Door to Light, as King Mickey predicted, and the two return home, reuniting with their friends. While Sora shares a hug with Donald and Goofy, Riku shares his own moment with King Mickey. Ironically, even though Riku was once jealous of Sora's friendship with Donald and Goofy, he ended up having a similar one with Mickey.
 Kingdom Hearts coded
One of the memories hidden in the Journal depicts Riku meeting Ansem on Destiny Islands.
In the Destiny Islands room of the Dataspace's Castle Oblivion, Data-Riku reveals to Sora the memory of Riku on the Clock Tower.
After the Dataspace simulation finishes, King Mickey goes to talk to Yen Sid, who advises him to summon Sora and Riku for a Mark of Mastery exam. Mickey writes a letter to Sora, Riku, and Kairi, which he sends in a bottle to Destiny Islands. As they sit on the beach, Sora and Riku watch the waves and comment that Destiny Islands is a small world, but also part of a much bigger one, then jump to discussion about the Door to the Light. Kairi then appears with Mickey's letter, which the trio reads together.
 Blank Points
After reading Mickey's letter, Sora sits on the Paopu tree while holding it and staring off into the sunset. Riku walks up to him and asks if he has decided, and Sora says that he has. He later smiles at Sora's decision to venture out to find those connected to him.
 Kingdom Hearts 3D: Dream Drop Distance
Riku accompanies Sora to the Mysterious Tower in response to a call from Yen Sid to undertake the Mark of Mastery exam in order to prepare for the coming return of Master Xehanort. Once told of the threat Master Xehanort poses, Riku does not hesitate to take the exam, seeing it as an opportunity to see whether or not he is worthy of wielding the Keyblade, especially after his past with the darkness. For their exam, Riku and Sora are sent to the Sleeping Worlds, where they are to awaken several worlds that were restored following the defeat of Ansem but remained in a state of deep sleep.
Riku and Sora's journey starts on Destiny Islands, but they soon move on, and end up in Traverse Town, where Riku ends up separated from Sora but discovers his new attire and abilities. After meeting up with Joshua and his friends, who tutor him, Riku sets off on his journey alone, venturing across several worlds, meeting new friends and battling new villains. But along the way, Riku comes into conflict several times with a mysterious young man with ties to Master Xehanort, accompanied by Ansem himself, who remind Riku of his past experiences with the darkness and try to get him to succumb again, but Riku refuses, reminding Ansem that he walks the road to dawn.
However, once all the seven Keyholes in the Dreaming Realm are sealed, Sora ends up trapped in sleep in The World that Never Was, and Riku rushes to his rescue upon realizing this. He finds Sora in a comatose state inside the Castle, his heart having been damaged by Xemnas and the young man himself. The young man turns out to be an alternate timeline incarnation of Master Xehanort in his youth, who has been traveling to different periods in time to recruit several other incarnations of Xehanort together. Riku attempts to awaken Sora, but the darkness from Sora's nightmare turns into the Anti Black Coat that engages Riku. Riku manages to defeat the Anti Black Coat and carries on through the castle, eventually coming face to face with Ansem. Ansem reveals that Riku is actually a Dream Eater, and, over the course of the exam, has been purifying Sora's dreams of Nightmares. Ansem attempts to take over Riku's body again, but remembering his secret encounter with Terra, Riku resolves to make his inner darkness his own power for good and make Ansem become part of his light. Then the two battle each other once more. Ultimately, Riku prevails and eventually makes his way to Where Nothing Gathers, where he finds Sora on an Organization XIII throne. Young Xehanort blocks Riku's way, but Mickey comes to Riku's aid by casting a Stopza spell. Young Xehanort, however, is unaffected by the spell and knocks Mickey aside to battle Riku. After a fierce struggle, Riku defeats Young Xehanort. However, the victory is short-lived, as Master Xehanort is finally revived and joined by the rest of his new Organization, among them are Young Xehanort, Ansem, and Xemnas.
Master Xehanort fills Riku and Mickey in on his past attempt to create the χ-blade by pitting Ventus and Vanitas against each other. The plan failed, but he had a backup. Master Xehanort had Young Xehanort create a new Organization XIII made of Master Xehanort himself and twelve vessels to harbor a piece of Master Xehanort's heart in order to create thirteen darkness to battle seven lights and recreate the χ-blade, the twelfth intended vessel was to be Riku but since he built a resistance to darkness, Sora was forced to replace him. Riku and Mickey attempt to save Sora, but are restrained by Ansem and Xemnas. Lea then arrives and saves Sora from Master Xehanort. Ansem summons his Guardian, who grabs Riku and Mickey, but the Guardian is defeated by Donald and Goofy, who arrive via Mickey's old Star Shard. His plans temporarily derailed, Master Xehanort retreats with his Organization.
Riku brings Sora's comatose body back to the Mysterious Tower and dives into Sora's body to mend his fractured heart. In the process, he is forced to battle Sora, clad in Ven's Keyblade Armor, which has been corrupted by a Nightmare. Riku defeats the Nightmare and uses Sora's Keyblade to enter a memory of the Destiny Islands, deep inside Sora's heart. Here he meets projections of Roxas, Ventus, and Xion, who each ask a question before disappearing. After answering the three questions, Riku finds a bottle in the surf, and a data projection of Ansem the Wise approaches him. Ansem tells Riku about the research data he hid inside Sora while he was asleep, the content of the bottle, and he talks about Sora's ability to connect with others' hearts, and how it may be able to bring back those that have been lost. He tells Riku that by defeating the Nightmare and answering the three questions, he has successfully awakened Sora. Riku returns to the real world, reuniting with Sora and the others, and Yen Sid names Riku as a Keyblade Master. Riku and the other are shocked when Lea vows to catch up with him, reveals his plan of becoming a Keyblade wielder, and successfully — albeit accidentally — summons his Keyblade.
As his first duty as a Keyblade Master, Yen Sid orders Riku to bring Kairi to him to undergo training with her Keyblade in order to counter Master Xehanort's new Organization.
 Other appearances
 Final Fantasy XIII-2
Riku's iconic scene in Kingdom Hearts where he reaches for Sora to follow him, later echoed by Vanitas and Young Xehanort, is emulated in a scene in Final Fantasy XIII-2; in a dream version of New Bodhum, Serah finds Lightning on the dock, who beckons for her to stay, saying that her family is waiting. After refusing, Lightning is engulfed in chaos.
In Kingdom Hearts, Riku is a calm, cool, collected teen who is not afraid to go far beyond his limits. This shows through when he shows no fear in stepping into the dark portal when Destiny Islands was being consumed by darkness, along with his statement "I'm not afraid of the darkness!" Also, he seems to be aware of Sora's romantic feelings toward Kairi and often teases him for liking their friend, such as when he challenges Sora to a race, Sora saying that if he wins, he gets to become captain of the raft they're constructing; Riku ups the ante by saying that if he wins, he gets to share a paopu fruit with Kairi. However, he reveals that he only made that bet to see the reaction on Sora's face, which shows his awareness of Sora's feelings for Kairi.
He also shows a strong competitive streak, along with a bit of jealousy when he challenges Sora, saying that his heart is stronger than Sora's heart. It is not actually said aloud, but thanks to Maleficent, he became increasingly jealous of Sora, starting with him finding out about Sora's new friends, and his thinking that he had been replaced. The jealousy grew when he learned about Sora possessing the Keyblade, and eventually turned into rage, resulting in the battles against Sora throughout Kingdom Hearts, and his possession by Ansem, Seeker of Darkness.
Though his traits were not too favorable in Kingdom Hearts, he becomes more heroic in Kingdom Hearts: Chain of Memories. Riku has many realizations. One of these was him realizing that he let his heart become weak. From that moment on, he began to shy away from the darkness in his heart. Through the scores of fights and battles in Castle Oblivion, he makes another big realization: he can't get rid of the darkness in his heart, and decides to use it without turning from the light like before. He matured immensely, and along with leaving his past behind him, he also left a lot of his unfortunate traits.
In Kingdom Hearts II, he shows a great amount of loyalty and care for his friends. To save Sora, he did everything he could to bring Roxas to DiZ to make Sora whole again, going so far as to give up his physical form for that of Ansem. As Sora journeyed on between the worlds, he dropped him some valuable clues, such as the sea-salt ice cream and the picture.
When he finally is found in the World That Never Was, he repeatedly shows regret, telling Sora that he didn't want to be found, and almost refusing to come back to Destiny Islands because of his wrongdoings.
Ever since he was young, he had been curious with everything that is outside of his world. Over time, his curiosity became obsession and he began to think of his world as a prison surrounded by water. This obsession greatly diminishes throughout the year of Sora's slumber, most likely because he had already seen many other worlds that the curiosity disappeared. When he returns to Destiny Islands in Kingdom Hearts II, he still comments it as a small world, but agrees with Sora's remark that it is only a part of one that's much bigger. This marks that Riku has a better view of his home world than before, when he imagined it as a prison.
Another good personality trait he shows is a strong protectiveness over his friends. He never wanted Sora and Kairi to find out about the time he spent in the darkness. He nearly sacrificed himself to protect Sora from Xemnas' attacks, leaving him injured after the final battle.
Though Riku matures significantly over the course of the series, he still seems to retain some of his old Kingdom Hearts self, particularly his sense of humor; he refers to Sora, Donald, and Goofy as "wise guys" when talking to the Emperor, cracks a joke about Donald and Goofy's intelligence at their expense, and calls Sora a "total sap" when going to confront Xemnas.
Like Sora and Roxas, Riku can wield the Keyblade, though he can wield both his own and others since Terra chose Riku to inherit the Keyblade in Kingdom Hearts Birth by Sleep. In comparison to Sora's two-handed style and Roxas's dual-weaponry, Riku attacks with a fast one-handed style with his Soul Eater/Way to the Dawn. Riku attacks very quickly with either weapon in combat, and is adept with his weapons being just as able with his weapons as Sora is with his. His strength and agility are best demonstrated on Destiny Island, where he is known as the strongest child on the island (Tidus remarked that he, Wakka, and Selphie were defeated by him even after they triple-teamed him), and possesses an athletic springing kick if knocked down. Though Sora has bested Riku on several occasions, it is still unclear who is truly stronger. Riku is also shown to be skilled in hand-to-hand combat, as shown in Kingdom Hearts 358/2 Days, in which he easily knocks down a charging Xion with a single punch after dismissing his Soul Eater weapon. Riku showed another glimpse of his strength in Kingdom Hearts 358/2 Days by defeating Xion with ease and holding his own against Roxas. Riku's strength is acknowledged in Kingdom Hearts II, when Roxas tells Sora during battle that he has defeated Riku - when Sora repeats Roxas's claim to Donald and Goofy, Donald exclaims "But nobody could defeat Riku!", and Sora agrees.
At first, Riku had no powers whatsoever, although he was a rather strong individual. After arriving in Hollow Bastion he gets his weapon, Soul Eater. It gave him a slight increase in power, but as seen in the battle versus the Parasite Cage, he was only slightly more powerful than on the islands.
Sometime after Monstro, Riku made a pact with Maleficent. This gave him three new abilities: The ability to summon and control Heartless, the power to traverse the worlds using Corridors of Darkness, and finally the ability to craft Anti forms. He demonstrated the first two abilities several times, and the third he used on Sora to create many AntiSoras and one complex one wielding a shadowy Keyblade.
After Sora left Neverland, Riku returned to Maleficent who gave him a large increase in his dark abilities. This allowed him to draw on dark energies to increase his physical power and clothe himself in an organic-looking suit of darkness. While in this Dark Mode he could zip around the battle field at an incredible speed and each blow from his Soul Eater dealt large damage. However, this form was taxing on his heart as seen after his battle with Sora in Hollow Bastion.
It is revealed that Riku was to be the original recipient of the Keyblade, but when he opened the Door to Darkness in Destiny Islands, plunging that world into Darkness, it instead chose Sora. However, in Hollow Bastion, Riku took the Keyblade from Sora by using the sheer strength of his heart, though when he uses the darkness within himself, his power over the Keyblade weakens and it returns to Sora who had proven the strength of his own heart.
When Ansem, Seeker of Darkness, possessed his body he gained incredible new powers, but he was now stuck permanently in dark form because of the darkness pouring out of him. In addition, he took six of the seven Princesses' hearts and used them to form the Keyblade of People's Hearts. Riku's enhanced dark powers under possession are Dark Raid, where he throws a spinning Dark Keyblade, Dark Break where he performs a powerful jump attack, Dark Firaga where he counters a spell by shooting an orb of dark energy, and Dark Aura where he dashes around the arena at high speed slashing all in his path.
When he is playable in Kingdom Hearts: Chain of Memories, he is given a preset deck in each world that cannot be changed and changes automatically during gameplay. By breaking his opponent's cards, Riku acquires "DP", which let him transform into Dark Mode. Dark Mode, along with giving him increased speed and increased strength, gives him access to sleights that mimic his special attacks from Kingdom Hearts. Outside of Dark Mode, any combination of stocked cards counts as a sleight and costs Riku a card, so he cannot perform combo attacks as easily as Sora can. Instead, he has access to a unique system of battle called "card dueling", which allows Riku to stun opponents and perform special commands by breaking their cards multiple times.
Overall, in contrast to Sora who must rely on sleights and combos to fight, Riku's playing style is more up-front, relying on card duels and breaks to acquire DP and enter Dark Mode. In this game, Zexion said his scent is very similar to the Superior's. In gameplay, it is also shown that Riku can run faster and jump higher than Sora.
At the end of Kingdom Hearts 358/2 Days, he used the power of darkness to help him defeat Roxas. This surge of power distorted his physical form, causing him to appear identical in appearance to Ansem, Seeker of Darkness. While trapped in this form he could use Xehanort's Guardian and use some of Ansem's attacks for a limited time in addition to his other powers. Riku's power increased in this form shown when he easily defeated Roxas as well as easily overpowering Saïx, forcing the latter to flee.
Riku's Soul Eater changes into Way to the Dawn sometime between the second visit to Land of Dragons and The World That Never Was. When he turned into his "true form" in the end of Kingdom Hearts II, his powers of light increased dramatically while his powers of darkness decreased. As a party member, Riku possesses various abilities that combine his dark powers with Sora's light powers. Riku can use a new Dark Aura that fires Dark Firaga orbs that inflict a Stop effect whenever Sora completes a combo, Dark Shield to project a barrier of darkness, as well as to numerous other powers. In his Limit with Sora, Eternal Session, Riku is able to project waves of dark energy from his Keyblade in addition to unleashing fast combos and Dark Firaga barrages.
At the end, Sora and Riku toss their Keyblades together to act as a super-damaging magnet. It should be noted, though, that despite the fact that Riku is a wielder of the Keyblade, he can't use any of Sora's keychains while he is in the party. Also, Riku is one of the three only characters shown being able to summon more than one Keyblade at once, the other two being Roxas and Sora.
 Kingdom Hearts
In Kingdom Hearts, Maleficent gives Riku the power to control the Heartless for a short time. Later, Maleficent unlocks his dark powers which he has used throughout the series. Ansem, Seeker of Darkness possessed Riku and gave him all of his power. In Kingdom Hearts: Chain of Memories, Riku was able to escape the Realm of Darkness through the subconscious use of his dark powers. Riku also gained full control over his dark powers and finally defeated Ansem.
 Kingdom Hearts: Chain of Memories
 Kingdom Hearts 358/2 Days
Riku's Limit Break, Darkstrom, is very similar to his Dark Aura Sleight from Kingdom Hearts: Chain of Memories. During Darkstrom's execution, Riku will rush at the enemy multiple times, similar to Sora's Sonic Blade ability. His Final Limit infuses his weapon with light energy as he wildly slashes about.
 Kingdom Hearts II
As a party member, Riku is very similar to Beast from Kingdom Hearts, in the sense that he is the final party member, as well as the strongest. He has high strength, magic, and above-average defense. He has some of the best abilities such as MP Hastega. Furthermore, his main action abilities, Dark Aura and Dark Shield, are activated upon the player's command, which helps him conserve MP for Cure Potion, which fully heals the party. Riku's greatest asset is his Limit, Eternal Session, which is tied with Sora's Trinity as the best Limit in the game. He can equip one accessory and two armor pieces. Riku's abilities are as follows:
Riku is also temporarily playable during the final battle with Xemnas. During this time, he has only three commands - Dark Aura, Attack, and Jump.
 Kingdom Hearts 3D: Dream Drop Distance
When Riku and Sora enter Sleeping Worlds, Riku unknowingly enters Sora's dreams. In doing so, he takes on the role of a Spirit Dream Eater. He has the ability to fuse with Spirits in his party, letting him use Link Styles.
Unlike Sora, Riku uses many Dark-type techniques, like Dark Break, Dark Aura, and Dark Splicer. He also shares many exclusive combat commands with Terra from Kingdom Hearts Birth by Sleep, such as Zantetsuken, Sacrifice, Meteor, Limit Storm, and Meteor Crash. He uses similar action commands to Aqua, such as Dark Barrier and Doubleflight.
 Notes and references