Sho, a student who is retaking entrance exams, suddenly receives a phone call. The voice is from his childhood friend Ran, who used to live next door. She is also a retake student and wants to stay in Sho's room to take winter courses. When he meets Ran again after a long time, she still has the same appearance as before, but she has grown into a beautiful busty girl that is hard to believe that he used to tease her about being small. In her defenseless loungewear, Ran shows off her big breasts and seduces Sho, leading to a sweet and sour erotic life!