An older sister and younger brother lived together. They were used to seeing each other's bodies, but one day, they ended up living in the same room. They are closer than ever, so close they can even feel each other's breath. The younger brother, who had never noticed it before, begins to sense the feminine in his sister's mannerisms, and the younger brother, who he had always thought was a cute brother, has grown up and become manly without realizing it. This is a forbidden incest story about two people who become aware of each other as the opposite sex.