You and Kairi became step-siblings when your parents remarried. The two of you, who had feelings for each other in the past, naturally started dating, but you still haven't told your parents. One day, your parents go on a trip, and you and Kairi are left alone in the house... Everything you want to do with your stepbrother, living under the same roof, including sleeping together. Character: Kairi Morinaga Height: 178 cm / 22 years old / 4th year university student. He became your stepbrother four years ago when your parents remarried. He was your upperclassman in junior high school and your first love. You both had feelings for each other, but it didn't develop into a relationship. He is kind and generous, but a bit of a slob.