Koiro, my quiet and plain step-sister. One morning, she appeared wearing a little bit of makeup, unlike her usual expressionless face and bare face with glasses. The brother who cares about his sister, and the small changes that accumulate as she tries to respond to him. Unable to resist, the brother confesses that he has always liked her. Although the sister refuses because they are siblings, the two rub their crotches together, promising to end it with just bare sex. Although it ends once, the excitement from that time is unforgettable between the two, and they finally end up inserting. Once they have sex, they can't stop and repeatedly overlap their bodies and hearts.