Hisagomaru

In manifested form Hisagomaru resembles a small white automaton, its body a cylindrical trunk topped by a rounded head. Thin limbs end in flat hands and feet, a plain rectangular slot serves as a mouth, and a single black circle stands in for his right eye. Where a left eye would sit, a tall vertical gauge lined with measurement marks stretches down most of his face.

Hisagomaru is deeply shy, dwelling in the tunnels beneath the Seireitei and bolting at the sight of others. He apologizes almost compulsively, flustering through questions rather than answering them, and he flatly refuses to kill any creature for food. That timidity gives way to bravery when it truly counts, and he single-handedly brings down the Tentacle Tōjū after the other fighters have fallen. He harbors no grudge against Hanatarō Yamada, having tried again and again to slip back into his sword before wrongly concluding he had been abandoned.

Forcibly given a body during the anime-only Beast Swords conflict, Hisagomaru struggles in vain to return to his blade and, believing Hanatarō has rejected him, withdraws to live alone in the waterways. Loneliness eventually drives him to pilfer things from the surface, including chickens Hanatarō is raising, which draws Soul Society's attention. When Hanatarō, Ikkaku Madarame, Hōzukimaru, and Nanao Ise track him down, the arrival of the Tentacle Tōjū prompts him to reveal his identity and crush the threat with his cannon. He is overjoyed to learn his master never forsook him, and once Renji Abarai defeats the final Tōjū, the fading energy sustaining the spirits returns Hisagomaru permanently to his sword.

His weapon heals rather than harms, filling the gauges on both the blade and his own face as it works. At capacity it becomes Akeiro Hisagomaru, whose chest splits open into a massive cannon that gathers every healed wound into one crimson blast, unleashed at the command to infuse.