"Tsuiraku JK to Haijin Kyōshi" centers on the relationship between a high school girl, Hoshino Sora, and her teacher, Haijin. Sora is a cheerful and popular student who hides her struggles with depression, while Haijin is a reclusive, eccentric teacher with a mysterious past. The story begins when Sora attempts suicide by jumping off the school roof, only to be saved by Haijin, who happens to be passing by. This incident marks the start of their unconventional bond.

Haijin, who is socially awkward and often misunderstood, becomes an unexpected source of support for Sora. Despite his abrasive demeanor and tendency to isolate himself, he recognizes Sora's pain and offers her guidance, albeit in his own unorthodox way. Their interactions are marked by a blend of dark humor, emotional vulnerability, and mutual understanding. As the story progresses, Sora begins to open up about her struggles, while Haijin gradually reveals fragments of his troubled past, which includes a failed career as a novelist and personal tragedies that led to his current state of isolation.

The narrative explores themes of mental health, loneliness, and the impact of human connection. Sora's journey involves navigating her depression while trying to maintain a facade of normalcy in school, while Haijin grapples with his own demons and the guilt of his past failures. Their relationship evolves into a complex dynamic that blurs the lines between mentor and friend, as they both find solace in each other's company. The story also delves into the lives of secondary characters, such as Sora's classmates and Haijin's colleagues, who provide additional layers to the narrative by highlighting societal pressures and the stigma surrounding mental health.

The tone of the series balances moments of levity with poignant explorations of its characters' inner struggles. Through its portrayal of Sora and Haijin's relationship, the manga examines the importance of empathy, understanding, and the ways in which people can help each other heal, even in the face of their own imperfections.