In a quiet, seaside town in the countryside where little ever seems to change, high school student Katsuhiko Haino navigates a year of his life marked by restlessness and stalled relationships. The setting is a sleepy port town modeled after Esashi in Hokkaido, characterized by winding roads overlooking the sea, a sense of stagnation, and a tight-knit community where the past and present constantly intersect. The story unfolds over approximately one year, with each of the single-volume manga's chapters titled after a successive month from April onward.

At the center of the story is Katsuhiko, a second-year student and number eight on the school’s rugby team, who is dating his classmate Reiko Arai. Externally, Katsuhiko has a life that seems enviable. However, he is plagued by a hollow selfishness and a persistent sense of ennui, feeling trapped by the very normality of his existence. His relationship with the demure and intelligent Reiko is a primary source of this frustration. Although they engage in intimate acts, Reiko is determined to remain a virgin until she graduates from high school, repeatedly refusing Katsuhiko’s advances for full intercourse. This boundary leaves Katsuhiko feeling that his girlfriend sees him as little more than an outlet for her own desires, further deepening his dissatisfaction.

The delicate status quo of the young couple is upended with the arrival of Manabu Izawa, a 25-year-old woman who becomes the new chemistry teacher at their school. An alumna of the same school and a former classmate of Katsuhiko’s older brother, Manabu takes up lodging in the detached annex of the Haino family home. This annex was previously the private space where Katsuhiko and Reiko would meet, and his initial reaction to her presence is one of resentment. Manabu is a tall woman, nearly 180 cm, who is often mistaken for a man. She is insecure, suffers from stage fright, and is deeply stressed by her life, a condition she drowns in heavy drinking. Despite their initial friction, Katsuhiko and Manabu develop an unexpected and easygoing friendship as drinking buddies, bonding over their shared sense of being stuck and their late-night conversations in the very room where he once met his girlfriend.

The narrative pivots on the complex and shifting dynamics of this love triangle. Manabu formulates plans to help Katsuhiko get closer to Reiko, while secretly beginning to develop feelings for the younger man herself. Meanwhile, Reiko grows increasingly suspicious, worrying that Katsuhiko is using her only for sex and fearing that he is having an affair with the new teacher living in his house. As the months pass, Katsuhiko finds himself torn between his obligation to his relationship with Reiko and his growing, more mature connection with Manabu.

The story reaches its resolution not with grand romantic gestures, but with the quiet, unglamorous drift of life. Katsuhiko eventually decides to confess his feelings to Manabu, but his timing is off. Manabu, in a final act of seeking stability, ends up in a shotgun marriage with a childhood friend named Nishi, the owner of a local sushi bar called Sushi Gen who had consistently worried about her drinking. Following this disappointment, Katsuhiko and Reiko part ways. After graduating from high school, Reiko moves to Tokyo to attend university, where she begins a new relationship with a former rugby club teammate. Katsuhiko, in stark contrast, remains in the seaside town, taking a job at the local town hall, a position that solidifies his unshakeable sense of being isolated and left behind. Adding to the sense of departure, even his own mother abandons the familial home to pursue her dream of becoming a novelist in Tokyo, leaving Katsuhiko utterly alone in the place where nothing ever seems to change.