The tsundere sister is mean to her brother in front of the rest of the family, but she secretly has sexual desires for him as he peeks at her panties and gets his dick hard. When her brother comes to the bathroom to get her even more excited, the perverted sister shows him her grown-up body in the bathroom. The two's sexual desire grows stronger day by day so that the other family members won't notice, and they end up touching each other secretly while the other family members are preparing dinner. Unable to hold back, the two lock themselves in the sister's room and devour each other's bodies, crossing the final line and having sex.