Mimuru belongs to a pacifist species of humanoid shape-shifters originating from an unspecified planet. Her people sustain themselves solely on vegetables and the regenerating tails of certain creatures, embodying their non-violent principles and balanced coexistence with their ecosystem.

Mimuru's community adopts Bander, a human infant, after his parents perish in a terrorist attack that destroys their spaceship; he arrives via escape pod. She aids in raising Bander for 17 years, embedding him in their culture and values. Pirates later assault her homeworld, compelling Mimuru to escape alongside Bander. During their involuntary voyage to Earth, she journeys with him as he unravels the mysteries of his origins and lineage.