After a bath, his older sister Misora wanders around the house in just a bath towel. To her younger brother Naoya, it’s a familiar sight, but Naoya’s friend Masayuki, who is visiting, is taken aback by the sight of Misora. Masayuki, who is not immune to women to begin with, can’t help but get aroused by Misora’s persistent physical contact. Whether he knows Masayuki’s feelings or not, Misora invites Masayuki to “come and stay the night tomorrow.” And the next day, Masayuki visits the Aoki household with a heavy heart, but…