Fenrir

 The Fenrir is a Keychain for Sora's and Player's Keyblades that appears in Kingdom Hearts II and Kingdom Hearts Union χ. The Fenrir is also one of the types of Keyblades left at the Keyblade Graveyard.

In Kingdom Hearts II, after defeating Sephiroth in Radiant Garden, Sora witnesses a battle between Cloud, Sephiroth, and Tifa. After Sephiroth and Cloud fly away in the middle of their duel, Tifa thanks Sora for his help and gives him the Fenrir Keychain.

Design
The Fenrir's design differs depending on the upgrade, most of which are seen in Kingdom Hearts Union χ. Unlike most other Keyblades, which are modeled after keys, the Fenrir is modeled after a  key.

The default Fenrir has a bronze appearance, with a green or a rusted bronze handle. Two rods jut out of the top of the guard, similar to the Fusion Swords' racks on Cloud's motorcycle from Final Fantasy VII: Advent Children. The blade is the shaft of a pin tumbler lock key, covered in bandages from the tip to the base. The Keychain is a dull bronze, with the token being Cloud's Fenrir pendant from his Advent Children outfit..

The first upgrade, also seen in Kingdom Hearts II, has a red handle similar to that of the Fusion Swords and a grey color scheme. The rods on the rainguard are longer, as is the blade. The bandages on the blade are mostly gone, except for the base.

The second upgrade is heavily inspired by Cloud's motorcycle. The guard is a dark grey, with some golden highlights on the sides. There are two rods on each side of the guard, bearing more of a resemblance to the Fusion Swords' holsters. The blade is now dark grey, almost black, and bears two pointed edges on the tip that resemble wolf ears. In addition, the bandages on the blade are gone, replaced a grey highlight at the base. The Keychain has a golden color scheme.

The third upgrade cloaks the Keyblade in a green aura.

The Keyblade Graveyard variant has darker bandages, and lacks a Keychain.

The Fenrir is named after Cloud's motorcycle 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. In the Dissidia series, Cloud also gains his own version of the Fenrir as one of his weapons.

Gameplay
In Kingdom Hearts II, 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 the Ultima Weapon.

The Fenrir is the only piece of equipment with the Negative Combo ability; in combination with the Negative Combo that Sora learns and a lack of equipped Combo Plus and Air Combo Plus abilities, Sora can attack with only 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.

Other Appearances
The Fenrir Keyblade is packaged with the Series 1 Play Arts Figures Valor Form figure.

Final Fantasy Record Keeper
The Fenrir appears as a 6★ Keyblade. It can be acquired from the Relic Draw during the Kingdom Hearts collaboration event. The Fenrir bestows the Arcane Overstrike Soul Break Ragnarok when equipped to Sora.