カノジョの姉は……変わってしまった初恋の人

High school student Ooshima Kamome got his first girlfriend. She is Shishido Himawari, a neat and reserved classmate. From now on, happy days for the two of them will begin. Just as that seems to be the case, Kamome reunites with his first love, Tsuyu, at Himawari’s house for the first time in several years.

Tsuyu, who has lost her bright and cheerful old self, has a decadent and dreary air about her. She has become Himawari’s sister-in-law due to her parents’ remarriage. The shock of the reunion is short-lived, as Kamome is taken into Tsuyu’s room without knowing what is going on.

「…Perhaps, it was your first time?」

I want you to return to the way you were when I liked you. Despite having a girlfriend, Kamome is slowly being consumed by his feelings for Tsuyu.

Is it pure love or obsession? This is a story of pure, straightforward, plundering love.