Kataoka Ritsuko

Mariko's biological younger sister, 36. Ryuichi's aunt, though she gets angry if you call her that.

Recently divorced, she shrewdly squeezed a hefty settlement out of her ex and used it to go on an overseas trip—a crafty woman.

Rents an apartment near the Iwamoto family, enjoying a carefree single life. She drops by casually, teasing Ryuichi for fun.

Unlike the reserved Mariko, she has a flashy taste, which often leads to arguments between the sisters.