Iwamoto Mariko

Ryuichi's stepmother, 38 years old. Ryuichi calls her “Mama.”

The stress she'd been bottling up over her husband's womanizing exploded when he vanished. She ended up having a physical relationship with her stepson.

That said, she sees it as “physical affection with my dear son” and doesn't seem troubled by it at all. In fact, she actively seems to enjoy it.

While she finds satisfaction in pleasing Ryuichi, specifically his lower half with her body, she also seems constantly worried that Ritsuko might be seducing her son.