"Happy Lesson" centers around Chitose Hitotose, a high school student who lives alone following the death of his parents. His solitary life takes an unexpected turn when five of his teachers, each representing a different subject, move into his home to act as his surrogate mothers. The teachers—Minazuki Rokumatsuri, Yayoi Shouji, Kisaragi Oboro, Haruka Amamiya, and Suzukaze Hazuki—are chosen by the school to provide Chitose with the care and guidance he lacks. Each teacher brings her own unique personality and teaching style, creating a dynamic and often chaotic household.

The narrative explores the daily interactions between Chitose and his new guardians, blending comedy, slice-of-life elements, and occasional moments of heartfelt drama. The teachers’ efforts to balance their professional responsibilities with their roles as caretakers lead to humorous and sometimes touching situations. As the story progresses, the relationships between Chitose and the teachers deepen, revealing their individual backstories and personal struggles. Themes of family, responsibility, and personal growth are woven into the plot, as Chitose gradually learns to open up and trust his new family.

The manga maintains a lighthearted tone, with episodic chapters focusing on the quirky dynamics of the household. The teachers’ distinct personalities—ranging from the strict and disciplined Minazuki to the carefree and mischievous Haruka—add variety to the interactions and keep the narrative engaging. While the series primarily emphasizes comedy and character development, it occasionally delves into more serious topics, such as the challenges of forming familial bonds and overcoming past traumas. The blend of humor and emotional depth makes "Happy Lesson" a multifaceted story that appeals to fans of both comedy and heartfelt drama.