Mizushima is a researcher (appearing only via holograms) responsible for working with Iceman. [From Wikipedia] Although he maintains a professional relationship with Iceman, upon learning that the research team plans to permanently refreeze Iceman, he betrays his fellow humans and helps Iceman escape to the surface, giving him the master key which would later become Eruruu's hair ornament. It is implied that he was eventually found out by the humans, although his fate is unknown.