Bakkōtō

The Bakkōtō is a rare class of weapon, its name playing on the idea of a beast-crossing or fused-tapir sword. It stands apart from the Zanpakutō in nearly every respect. Where a Zanpakutō is a symbiotic partner that strengthens as a Shinigami bonds with its inner spirit, a Bakkōtō behaves like a parasite, growing more powerful while it devours its owner until it corrupts the mind and finally consumes the person outright. Only a high enough level of spiritual power can hold that hunger at bay, and Rukia Kuchiki notes that the weapons are strictly illegal.

A Bakkōtō carries no known release states; instead it evolves in step with its wielder's Reiatsu. It can also be taken up by anyone possessing Reishi rather than being tied to a single Shinigami, so its strength and abilities shift from user to user. Each one includes an organic element, an eye that acts as its nucleus and a clump of flesh shaped like a mollusc's insides, which spreads across the wielder's body as it is fed more spiritual energy. A weapon has to be attached to this living core, and a Bakkōtō can grow stronger still by consuming the nuclei of others.

Bakkōtō are carried by the assassins serving Gyōkaku Kumoi and are produced through a secret method of the Kasumiōji Clan. They appear only in the anime.