After defeating Sephiroth in Radiant Garden, Sora witnesses a battle between Cloud, Sephiroth, and Tifa. After Sephiroth and Cloud fly away into a duel, Tifa thanks Sora for his help and gives him the Fenrir Keychain.
The Fenrir Keyblade, unlike all other Keyblades, takes on the appearance of a pin tumbler lock key, with bandages adorning the base of the blade similar to Cloud's buster sword. Its Keychain resembles Cloud's Fenrir pendant from his Advent Children outfit.
Fenrir is named after the motorcycle ridden by Cloud in Final Fantasy VII Advent Children, which also appears as a special Gummi Ship. The motorcycle is in turn named after Fenrir, a wolf summon which has appeared in multiple Final Fantasy games, in keeping with Cloud's wolf-motif. Fenrir is the shortened name of the Norse wolf-god Fenrisulfr.
Despite the passive ability of Negative Combo, the Fenrir Keyblade makes up for it with its high attack power. It is also the strongest Keyblade available; its strength even surpassing that of Ultima Weapon.
Fenrir is the only equipment with the "Negative Combo" ability, and if used with Sora's learned "Negative Combo" equipped and with all "Combo Plus" and "Air Combo Plus" abilities unequipped, Sora will exclusively use combo finishers. This makes it essential for high scores in mini-games like Junk Sweep, Cargo Climb, and Phil's Training, which focus on the use of combo finishers. Furthermore, as bosses in Kingdom Hearts II cannot be defeated unless a combo finisher is successfully performed on them, the Fenrir is quite useful against bosses who tend to interrupt Sora's combos.
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