The Irito family at night. For some reason, Mizuto's trunks were held in her daughter's hand. If Mizuto learns about this, he will be forced to become her "sister" with a penalty. Yui, who wants to avoid that, waits for Mizuto to fall asleep and heads to her dressing room in an attempt to obliterate her evidence. Then, Mizuto appears there. In that hand was a bra of a maiden ...