Bakkōtō

Seen only in the anime, the Bakkōtō is a scarce class of weapon carried by the killers in Gyōkaku Kumoi's service. Its forging is a closely held technique of the Kasumiōji Clan, and Rukia Kuchiki points out that owning one is entirely against the law. The danger of the weapon lies chiefly in what it demands of the person who wields it.

A Zanpakutō grows through the trust it shares with its Shinigami, but a Bakkōtō takes the opposite path, latching onto its user like a parasite. It gains power by siphoning their spirit energy, and in doing so it eventually clouds their mind and then swallows them entirely. Keeping that appetite suppressed requires a high enough reserve of spiritual power. The weapon knows no release states, expanding instead alongside the Reiatsu channeled into it, and because it responds to anyone who holds Reishi rather than a single bonded owner, its powers vary widely from one hand to the next. At its heart is an organic part, an eye that functions as the nucleus together with a fleshy mass like the innards of a mollusc, and this spreads over the wielder's body as it is fed. A weapon must be mounted onto the Bakkōtō, and one can be strengthened further by consuming the nuclei of its fellows.

Blades of this kind, Saiga among them, are borne by the assassins loyal to Gyōkaku Kumoi and are made by the Kasumiōji Clan through their guarded method.