Kozō is a water bear who was reborn in the Swamp of the Dead and bound to a Myriad Heavens Devouring System. He has eight sharp claws and terrifying mouthparts, and his body can grow large, initially reaching twenty meters and later over seventy meters after absorbing Hashirama cells. He is taken by the Slug Sage and forced to gnaw on tree bark, enduring life in the swamp. Later, he is summoned by Hashirama Senju and becomes a companion to Tsunade. He is closely monitored by Senju Tobirama, who suspects his origins. Kozō is cautious and clever, often pretending to be weaker than he is. He survives Tobirama's testing by bluffing about his past with the Slug Sage and gains access to Hashirama cells, which he absorbs to enhance his vitality and gain Wood, Water, Earth, and Yang Release nature transformations. He remains in Konoha, observing events and protecting Tsunade.
