Andou Rei

A third-year student at private Shirogane Academy. Her condescending and cold attitude at school makes her seem a bit isolated from others.
She's popular with boys but has few female friends.

She's quite intelligent, serving as the student council secretary, and isn't entirely without popularity. She's especially harsh towards her younger brother, Kei, to the point where others feel sorry for him.

She makes him run out late at night to buy sanitary products and even hits him (though she's not physically stronger than him).

Her father is often away on overseas business trips, and her mother is frequently occupied with work, leaving them to prepare their own meals. However, she dumps all the responsibility onto Kei.

Though she used to treat Kei as a stress-relief toy, one day, after her younger brother rebelled and she wet herself, she developed a masochistic streak.

Conversely, she ends up being trained by her younger brother, who has begun exhibiting sadistic tendencies.She starts deriving sexual pleasure from urinating in public.