Bakkōtō

The Bakkōtō is an uncommon breed of armament, appearing only in the anime, that Kumoi's killers take into battle. Each one is produced through a guarded method belonging to the Kasumiōji Clan, and Rukia Kuchiki flags the whole class of weapon as strictly forbidden. What sets it apart is less how it strikes and more the bargain it forces on whoever picks it up.

Where a Zanpakutō lives in partnership with its Shinigami and matures as the bond between them deepens, a Bakkōtō behaves like a parasite. It swells in strength by draining its owner's spirit energy, and as it does so it begins to gnaw at their sanity before finally consuming them whole. Only a wielder with plenty of spiritual power can keep that hunger in check. The weapon has no set release forms and instead grows in step with the Reiatsu poured into it. Unlike a Zanpakutō, which answers to one Shinigami alone, a Bakkōtō will serve anyone possessing Reishi, and its abilities differ from bearer to bearer. Each carries an organic core, an eye that acts as its nucleus joined to a fleshy, molluscan mass that spreads along the user's body as it is fed, and a blade or other weapon must be fitted to it. One Bakkōtō can even become more powerful by devouring the nuclei of others.

Bakkōtō such as Retsurai are wielded by the assassins serving Gyōkaku Kumoi and are forged by the Kasumiōji Clan through their secret craft.