The Fenrir is one of Sora's Keyblade in Kingdom Hearts II. After defeating Sephiroth in the 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. It is the KHII equivalent of the Metal Chocobo and One Winged Angel.
The Fenrir Keyblade takes on the appearance of a pin tumbler lock key, with bandages adorning the base of the blade similar to Cloud's sword. In this, it is notably the only Keyblade with no "teeth". Its keychain resembles Cloud's wolf pendant from his Advent Children outfit (also a reference to the wolf-god, Fenrir).
Despite the passive ability of Negative Combo, the Fenrir Keyblade makes it up for its high attack power. It is also considered to be the strongest Keyblade available, even surpassing that of Ultima.
Fenrir is the only equipment with the "Negative Combo" ability, and if used with Sora's learned "Negative Combo" equipped and all "Combo Plus" and "Air Combo Plus" abilities unequipped, Sora will exclusively use combo finishers. This makes it pretty much required for 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 like to interrupt Sora's combos.