I, Shibata Ippei, am a second-year high school student. Just before summer holiday, I decided to confess my feelings to my childhood friend, Shirai Miho, as it was my last chance to have fun together before the university entrance exams. However, she was already dating a handsome guy from the same class as her who was in the football club. I was feeling down, but Miho’s mother, Haruna-san, comforted me. During that time, she made an astonishing proposal. “I’ll…become your girlfriend, Ikkun.” She felt responsible for her daughter Miho hurting me, and she wanted to take responsibility for it. She said she would become my girlfriend for the duration of the summer holiday. Haruna-san is in her forties but could easily pass for someone in her twenties. She is beautiful, has an outstanding figure, and is well-endowed. Ever since I met her when I was little, she has been a divorced single mother. So, age difference is about the only thing to be cautious about. But I won’t cross any lines. After all, we’re just doing something lover-like. However, this summer, my fate and life will change drastically.