Hiyori Fujisaki, a third-year middle school student, has a crush on Yuuma Mizuno, the most popular boy in her grade. When classroom seats are rearranged, she finds herself sitting next to Karen "Ren" Sasamoto and in front of Kotone Kanbara, both of whom are Mizuno's childhood friends. Learning of their connection, Hiyori asks Sasamoto for his help in getting closer to Mizuno. Though reluctant at first, Sasamoto eventually agrees.

The situation quickly becomes tangled. Hiyori discovers that Mizuno has feelings for Kotone, not for her. At the same time, Sasamoto realizes he has secretly had feelings for Hiyori for over a year. Kotone, who has always been fiercely protected by Sasamoto, grows jealous of the bond forming between him and Hiyori and begins scheming to drive them apart. Despite these obstacles, Hiyori comes to reciprocate Sasamoto's feelings, and the two begin dating. Kotone, in turn, starts a relationship with Mizuno.

The story follows the four friends into their first year of high school, where the fragile peace shatters. Kotone dumps Mizuno and sets her sights on stealing Sasamoto back from Hiyori through manipulation and sabotage. The ensuing conflict grows increasingly bitter and destructive. Mizuno develops genuine feelings for Hiyori, leading to a complicated love polygon. The drama escalates when Hiyori becomes pregnant with Mizuno's child and subsequently suffers a miscarriage, a traumatic event that forces her to transfer schools and nearly results in Sasamoto's expulsion.

Years later, after enduring these intense trials of heartbreak, jealousy, and betrayal, Sasamoto and Hiyori ultimately find their way back to each other and are married. The narrative explores themes of friendship, unrequited love, and the painful transition from adolescence to young adulthood.