Bakkōtō

are a rare type of weapon used by Gyōkaku Kumoi's assassins. This type of weapon differs from the Zanpakutō in several ways. While the Zanpakutō is a symbiotic being, working and growing more powerful as the Shinigami develops a relationship with the sword's inner avatar, the Bakkōtō is more of a parasite, gradually consuming the user as it grows in power, until it starts to affect his mind and eventuallly devours him. Also, the Bakkōtō do not have any sort of known release states, instead evolving with the user's reiatsu. Finally, while Zanpakutō can only be wielded by their respective Shinigami, a Bakkōtō can be wielded by any person with reishi and varies in power and ability depending on its wielder. It is unknown how a Bakkōtō is formed, however, it is known that Bakkōtō are forged through a secret technique of the Kasumiōji clan. Rukia noted that the Bakkōtō are highly illegal.

Bakkōtō take the form of weapons with an organic component which consists of an eye (shown to be its nucleus) and a mass of flesh resembling the innards of a mollusc, which extends along the user's body as they feed it with more of their reiatsu.

Saiga
has the ability to momentarily paralyze opponents by reflecting moonlight into their eyes, leaving them unaware that any time has passed. If the user's reiatsu is great enough, it gains the ability to create an alternate dimension in which the opponent is left conscious but unable to move. If the user channels still more reiatsu into the weapon, he/she can create illusions based on the targets' memories, trapping them until their souls are crushed. At full power, it is able to shoot energy bolts similar to Getsuga Tenshō blasts. Saiga was first used by an unnamed assassin, and then by Hanza Nukui against Ichigo Kurosaki.

Kakuyoku
appears as an oversized guandao. When swung, it fires energy blasts which solidify into rock walls. It also allows the user to merge with the walls and hide for a surprise attack. Kakuyoku was used by an unnamed assassin, and then by Genga against Yasutora Sado.

Retsurai
takes the form of a "reaper" scythe, with protrusions over the edges. When a piece of its blade is eaten it causes blades to form on the user's back which can be fired at will. If eaten again it will refill/add to the blades. At all times, it causes spikes to grow from the user's body and seems to increase their speed tremendously. Retsurai was used by Jinnai Dōko against Rukia Kuchiki.

Shiragiri
takes the form of a "normal" katana with protrusions along the edge of the blade. Shiragiri has the ability to create mist, and can use its Infinite Corridor technique to turn the user into mist as well and solidify so it can attack. Shiragiri was used by Ryū Kuzu against Uryū Ishida.

Makoto Kifune
The nucleus of Kifune's bakkōtō grows on his left arm, while the rest of it covers his zanpakutō, allowing him to telekinetically control the blade at any direction and spin it like a saw blade.

Shūsuke Amagai
Amagai's bakkōtō takes the form of a tuning fork with the nucleus at the hilt. When used it emits large waves of reiatsu powerful enough to destroy one of the dimensional cleaners in the dangai. Its true form, however, is shown where it covers the right arm and shoulder in black armor. When in use it extends down and forms a blade of highly concentrated reiatsu, otherwise it wraps around his chest and forms a tail. When the blade is stabbed into the ground, the special abilities of zanpakutō in the area other than the user's are negated for a while.

Unnamed Assassins
The Bakkōtōs used by the unnamed assassins hilts are made of the tentacle like substance the other Bakkōtōs are known for. Their blades are similar to a normal zanpakutō but have an odd spike going down from the tip of the blade. Their ability is to possess the assassins bodies forcing them to fight even after a fatal blow. The only known way to stop the possessed assassins is to destroy their bodies.