Konomi ja Nai kedo 1

The siblings fight each other every time they meet. They get along so poorly, that they even start fighting in front of each other’s friends.
One day, Ritsuki comes home in a hurry in the rain and bumps into Kyouya at the entrance. Ritsuki gets angry, but freezes when she sees Kyouya’s shirtless and wet body. His body was muscular, which Ritsuki liked. When Ritsuki noticed that she was staring at Kyouya, she tried to quickly leave, but she bumped into Kyouya and sprained her leg.
Kyouya enters Ritsuki’s room with a compress and a bandage, and becomes conscious of the fact that he is of the opposite sex as he enters his sister’s room for the first time in several years. Kyouya tries to shake off his thoughts and leave the room before things get complicated, but Ritsuki demands that he give her a massage. Kyouya reluctantly decides to comply with her request out of guilt for causing her injury, but he notices this while massaging her… That his sister’s body is what he likes.