Sephiroth is the embodiment of Cloud's darkness. He, along with Cloud, Tifa, Aerith, Yuffie, Zack, and Cid, originate from the Squaresoft game Final Fantasy VII, where he served as the main antagonist. Sephiroth is the only Final Fantasy villain so far to appear in the Kingdom Hearts series.
Sephiroth originally appears as an optional boss in the international version of Kingdom Hearts, and was retained for the Kingdom Hearts Final Mix version of the game, which also added a short scene between him and Cloud. In Kingdom Hearts II, his role was greatly expanded and he was given a short side-story featuring him, Cloud, and Tifa.
While Terra is in Olympus Coliseum, Zack reveals that he aspires to become a hero like "another", referring to Sephiroth. Later, after Master Xehanort's defeat, a black feather falls before Zack as he watches Hercules train, hinting at Sephiroth's presence.
 Kingdom Hearts
Sephiroth appears within the Platinum Match at Olympus Coliseum, and after a difficult fight, Sora narrowly seizes victory. As Sora leaves the stadium, Cloud enters. Sephiroth invites Cloud to turn to the darkness, but Cloud refuses, launching a high-speed aerial battle whose outcome is not seen.
 Kingdom Hearts II
Right before the invasion of Hollow Bastion, Cloud warns Sora and company about Sephiroth, and his ways of the darkness. Later, as Sora exits the castle to go help defend against the invasion, Sephiroth appears. He asks about Cloud's whereabouts, and although Sora says nothing, Donald and Goofy retort that Cloud realizes that Sephiroth is the manifestation of his darkness. Seeing that Cloud is becoming enlightened and desires to fight him, Sephiroth takes his leave.
During the battle, Cloud is surrounded by Heartless, but Sephiroth intervenes, defeating them all in one slash. Cloud intends to defeat his nemesis to escape the darkness, but Sephiroth only replies that Cloud will never be able to do so, and will always cower in the light. Cloud vehemently denies his dark half's claims, but Sephiroth is undeterred, and leaves just as Tifa arrives.
After the Master Control Program is defeated, Sora encounters Sephiroth at the Dark Depths at Hollow Bastion. The villain again asks about Cloud, but Sora and his companions do not reveal anything. He then inquires about Sora, Donald, and Goofy's identities, but again, they refuse to answer. Sephiroth then notices Sora's Keyblade, and attacks, intending to test Sora's power and that of the Keyblade. Even though Donald and Goofy are with Sora when he confronts Sephiroth, they do not fight with him, since Sephiroth only wishes to battle the Keyblade master. Sora appears to overcome him, but Sephiroth just shrugs off the battle. Sephiroth compliments Sora on his skill with the Keyblade but says that Cloud is the only one that can "eliminate him". Sephiroth then tells Sora to find Cloud so that they can settle their feud.
Cloud arrives later, and they initiate a battle, with Sephiroth desiring to draw Cloud into the darkness. However, Tifa protects Cloud, saying that Cloud does have light in him, and that, even if he doesn't, then he just needs to be surrounded by light. Nevertheless, Sephiroth and Cloud start off for another battle, and after Tifa's intervention, Cloud glows in light, surprising Sephiroth and letting his guard down. The two disappear in a brilliant flash of light.
Sephiroth's appearance in both Kingdom Hearts and Kingdom Hearts II is largely the same as his appearance in the various games of the Compilation of Final Fantasy VII, though with a few significant differences. He has his distinctive long, silver hair with long bangs that frame his face, and dresses in a black leather coat. The coat has a large collar that reaches his ears even when folded back and is kept closed by a black belt with a silver buckle around his waist. Unlike in the Final Fantasy games, Sephiroth's coat has red-violet lining in the front. It is also noticeably more tattered in the Kingdom Hearts games. In Kingdom Hearts, Sephiroth also has regular blue eyes, unlike the green, catlike eyes he and his Remnants have in the main series. The sleeves of his coat end in metal rings in place of normal cuffs, and he wears black leather gloves. For some reason there is an odd, black and red, fin-like growth on his right forearm. Sephiroth's face looks strikingly like Cloud's, which is something that Goofy comments on in Kingdom Hearts II. This similarity would explain Sephiroth's difference in eye color from his original incarnation.
Sephiroth's chest is exposed, showing that he wears some sort of grey strap around his abdomen with two black belts over it, as well as two brown, overall-esque straps that intersect over his chest. He wears black pants and knee-high boots of the same color, with two grey belts wrapped around each boot. His eyes are blue and he wears a silver pauldron over each shoulder. In both games, Sephiroth sports a large, navy blue wing on his right shoulder, a design feature that has carried over to several characters associated with Jenova in the Compilation of Final Fantasy VII. In Kingdom Hearts II, he gains two more wings of the same color sprouting from either of his hips. Also in both games, Sephiroth carries his iconic sword, Masamune, as his weapon. Sephiroth is also one of only two characters who did not reappear in their Advent Children attire, the other being Cid.
Sephiroth's persona is one of cold ruthlessness. He is uncaring, having no sympathy for anyone but himself, laughing and grinning at Cloud, seeing him as almost no threat. Like many Final Fantasy characters, Sephiroth has been shown with stoic personality traits, along with a drawling voice. He is incredibly powerful, both physically and mentally, and is convinced that his power surpasses anyone else's. Almost emotionless, Sephiroth never overreacts to anything.
In all incarnations, Sephiroth is portrayed as a master swordsman, wielding a long blade known as the Masamune. In the Kingdom Hearts universe, Sephiroth has a large repertoire of techniques that reflects some of abilities he used in Final Fantasy VII. He can move about the battle ground with impressive speed, even fly, and occasionally teleports. He can also activate his attack "Stigma" which summons gigantic pillars of flames that can suck matter in, he can send out orbs of darkness called "Shadow Flares", and his most powerful attack "Super Nova" where he calls down meteors that spin around him and then explode.
His most noticeable technique is "Heartless Angel", an attack that drains Sora's MP and kills him instantly (unless Second Chance is equipped, in which case he will be left with 1 HP), if he is not interrupted in time; this is immediately followed by "Flash", which is fatal unless blocked via Reaction Command. He can also use a variation of Cloud's "Omnislash", in which he flies around the arena slashing wildly. In both games, all of his attacks are extremely powerful, being able to easily kill Sora even when he is maxed out in stats. Sephiroth has extremely high HP in both games. To add to the difficulty of him being a powerful enemy, in both games Sora has to fight him one-on-one without any help from his allies.
In Kingdom Hearts, Sephiroth is one of the hardest bosses, rivaling Kurt Zisa and Phantom; however, in Kingdom Hearts Final Mix, Xemnas, known at the time as "Unknown", also proved to be difficult. In Kingdom Hearts II, he is also one of the hardest bosses, having no true rival, standing out as the game's hardest boss. Kingdom Hearts II Final Mix also has the Organization XIII rematches and data battles, along with the Lingering Will, all of which are fights that greatly dilute Sephiroth's notorious difficulty.
 Magic Stats
In Kingdom Hearts, Sephiroth is immune to almost all forms of magic, although magic-based attacks such as Ragnarok do in fact cause damage.
In Kingdom Hearts II, all attack magic has no effect as well. The only magic based moves that will affect him are Magnega, the aftershock of Reflega, and the magic combo of Trinity Limit. In Kingdom Hearts II Final Mix, all Limits in Limit Form work well against Sephiroth.
Sephiroth debuted as the main antagonist in Final Fantasy VII. Once revered as a great hero, his discovery of the mysteries surrounding his origins and nature drove him to insanity. Easily recognizable by his foreboding appearance and frighteningly long sword, Sephiroth aspired to become a supreme being by using a destructive item known as the Black Materia to cast Meteor and devastate the world, wherein he would absorb the energy used to heal the Planet, and attain godhood. Constantly impeded by Cloud Strife, Sephiroth has seemingly grown a murderous obsession with him.
Almost all of Sephiroth's attacks, such as "Super Nova", "Heartless Angel", and "Shadow Flare", are named for attacks he uses in the Final Fantasy series. The few attacks he does not know in the Final Fantasy series, such as "Meteor" and "Flash", are still named for attacks in the series. Sephiroth's Kingdom Hearts appearance heavily influenced his attacks in Dissidia Final Fantasy, such as his Flash attack from Kingdom Hearts II appearing as "Oblivion", and his Shadow Flare using similar graphics as in the two Kingdom Hearts games in the original Japanese version of Dissidia. His Heaven's Light HP attack appears similar to his aerial combo in Kingdom Hearts II, and in his EX Mode Sephiroth takes on a purple aura similar to his aura when weak in the Kingdom Hearts series. Sephiroth also quotes or paraphrases many of his Kingdom Hearts lines, such as "It's time" (based on "The time has come") and "Know your place."
 Notes and references