I lost my mother at an early age and moved schools all the time because my father was transferred for work. During the summer vacation of my third year, I couldn't keep up with the classes and decided to attend a five-day summer course. Yumi-sensei, who was in charge of extra lessons, was pretty, kind, and somewhat like my mother. Then, through a sudden incident, we suddenly became close, and after class, we secretly made love to each other <covered in sweat in a classroom with a broken air conditioner>. However, I had to transfer schools again when my father was transferred for work...