"Happy Lesson" centers around Chitose Hitotose, a high school student living alone after the death of his mother. 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 (homeroom and Japanese literature), Yayoi Hakamada (science), Kisaragi Oboro (physical education), Haruka Amami (music), and Suzukake Hazuki (art)—bring their unique personalities and quirks into Chitose's life, creating a chaotic yet heartwarming household dynamic. Each teacher has a distinct background and set of challenges, which are gradually revealed as the series progresses.

The narrative unfolds through episodic arcs, blending comedy, slice-of-life elements, and occasional moments of drama. The teachers' attempts to care for Chitose often lead to humorous misunderstandings and misadventures, but their genuine concern for his well-being forms the emotional core of the story. Chitose, initially resistant to their presence, gradually warms up to his new family, finding solace and support in their unconventional arrangement. The series explores themes of family, belonging, and the importance of human connections, all while maintaining a lighthearted tone.

As the story progresses, the relationships between Chitose and his teachers deepen, with each character contributing to his growth and development. The teachers also face their own personal struggles, which are interwoven with their efforts to guide Chitose. The series balances its comedic moments with heartfelt interactions, creating a narrative that is both entertaining and emotionally resonant. Through its focus on the bonds formed within this makeshift family, "Happy Lesson" offers a charming and relatable exploration of the complexities of human relationships.