Mayama Ritsuki and Kyoya cross the line between brother and sister in the heat of the moment. They then realize that they like each other’s bodies. However, the situation remains the same, with them fighting every time they meet. On their first night together while their parents are away on a trip, they start fighting due to the tension of being alone together. Kyoya becomes sexually aroused by his sister’s gestures and tries to hide it by trying to run away from the scene. Ritsuki tries to catch Kyoya as he tries to escape, but he loses his balance and the two fall down in a tangle. A moment of silence continues with Kyoya on top of her… They want to touch, they want to be touched, their feelings overlap. On a night when their parents are away, there is nothing to stop them from being together.