A mysterious thief hounds the 4th Division barracks, where the Gotei 13 temporary headquarters are located. When Hanatarō Yamada's four chickens are stolen as well, Captains Kyōraku, Ukitake and Unohana decide to send an expedition into the sewers, where the tracks of the culprit lead.
The expedition includes Yamada, who knows the sewers like the back of his hand, 11th Division 3rd seat, Ikkaku Madarame and his Zanpakutō, Hōzukimaru, as the fighting force (just in case), and 8th Division's Lieutenant Nanao Ise (the team's leader).
The group soon trips two booby traps (thanks to Hanatarō), the last of which washes them into an unfamiliar part of the sewers, where Ikkaku is attacked and dragged away by a large tentacled creature. The others try to help him, but the creature submerges again and the resulting wave washes them away.
Back on the walkway, Hanatarō blames himself for Ikkaku's demise but Hōzukimaru reassures him that Ikkaku still lives. The team suddenly notices the smell of something cooking and go to investigate. They find a small tent with a barbecue burning at the front of it and a stand that contains many of the items stolen from the barracks. Hanatarō suspects the meat cooking on the barbecue came from his stolen chickens. A sound alerts them to the presence of a small figure wrapped in a torn robe, who turns to run as soon as he sees them.
Hōzukimaru and Nanao chase the creature towards Hanatarō and he trips and crashes into the latter's head. The robes removed reveal a small robot like creature with a gauge in the place of his left eye. Hanatarō thinks the creature looks familiar. Nanao and Hōzukimaru try to interrogate the creature but only manage to make him too nervous to answer their questions. The interrogation is cut short when an explosion tears through the wall and Ikkaku is hurled through it and lands next to them unconscious and in bad shape.
The tentacled creature from before is revealed to be a Tōjū. Hōzukimaru attempts to attack him using Bankai, but the blades just slip away, and the monster grabs him with one of its tentacles. Nanao hits it with Shakkahō, but the beast is unscathed and throws Hōzukimaru away. When Nanao is also grabbed by the Tōjū, Hanatarō is powerless to help, having left his Zanpakutō at his quarters.
The robot like creature grabs a katana, similar to Hanatarō's, and stabs Ikkaku with it. Instead of hurting him, Ikkaku's wounds are healed as the gauges on the sword and the robot's face fill. When the gauges are full, a flap in the robot's chest opens to reveal an enormous cannon that unfolds and with the command 'mitase, Akeiro Hisagomaru' a huge energy blast hits the Tōjū and destroys him. The strange robot creature turns out to be the materialization of Hisagomaru, Hanatarō's Zanpakutō. He believed his master has rejected him and left to live a life of recluse. He turned to stealing to relieve his loneliness and reveals that he stole the chickens to keep them as pets and that they are still alive.
The group returns to the surface and retrieves all the stolen goods, but Hisagomaru manages to lose his way and is left behind.