One night, Tachibana Kaoru, a second-year student at Aoba Dai-ichi High School in Minatocho, confesses her love to her middle school homeroom teacher, Shimotsuki Mirei, only to have her heart broken.
To make matters worse, the moment is witnessed by Minagi Shiori, a diligent classmate of Kaoru's and a model student.
On the brink of despair, Kaoru confides in Shiori about her painful past with Mirei.
Shiori listens silently and then enigmatically posits a peculiar question:
As their relationship blossoms, Inohara Riku—another student in the same grade and secret admirer of Shiori—also becomes involved, and the three begin to weave the tale of their summer together...