"Happy Lesson" centers around Chitose Hitotose, a high school student who lives alone following the death of his mother. His solitary life takes an unexpected turn when five of his teachers move into his home, each assuming the role of a mother figure. The teachers—Minazuki Rokumatsuri, Yayoi Takatsukasa, Kisaragi Amatsuki, Haruka Midorikawa, and Suzukaze Hazuki—represent different personalities and teaching styles, creating a dynamic and often chaotic household.

The narrative explores the daily interactions and challenges that arise from this unconventional living arrangement. Each teacher brings her own quirks and emotional baggage, leading to comedic and heartfelt moments as they navigate their roles as both educators and surrogate mothers. Chitose, initially resistant to the idea, gradually forms bonds with the women, who help him confront his past and grow emotionally.

The series balances slice-of-life humor with moments of introspection, delving into themes of family, responsibility, and personal growth. The teachers’ individual backstories are gradually revealed, adding depth to their characters and explaining their motivations for joining the household. As the story progresses, the relationships between Chitose and the teachers evolve, blending lighthearted comedy with occasional dramatic undertones.

"Happy Lesson" is structured around episodic arcs, with each chapter focusing on specific events or challenges faced by the characters. The manga maintains a lighthearted tone overall, though it occasionally touches on more serious topics such as loss, identity, and the complexities of human relationships. The interplay between the characters drives the narrative, creating a blend of humor, warmth, and occasional chaos that defines the series.