Aiko's mother. She is a part of the Cosmo Health Center organization. She is very strict with her daughter and keeps her on total control, often beating her up when she refuses to obey. After Hoshikawa Piroshiki's death, she cripples her leg, further enforcing Aiko to stay with her.

Spoiler

The crippling of her leg is actually a lie, as is revealed when Punpun and Aiko confront her that Aiko is leaving together with Punpun. Enraged with the news, she attacks Aiko with a knife several times, the biggest wound being around her abdomen. Filled with anger, Punpun assaults Mitsuko and strangles her to death.