Dad comes home from an “adult toy store” and hands his wife a chastity belt. She nods and turns to the couple’s 15-year-old son. “Let’s go,” she says. They disappear into the boy’s bedroom. The story begins with Japan’s obsessive exam culture. A boy’s whole future can depend on the senior high school he gets into. Some mothers will do anything to make sure their junior high school sons pass the all-determining entrance exams. Anything? Pretty nearly.