"Okusama wa Joshikōsei!?" centers on the unconventional relationship between a high school girl and her much older husband. The protagonist, Naoya Watarai, is a 26-year-old office worker who marries his childhood friend, Riko Izumi, a 17-year-old high school student. The story explores their daily lives as they navigate the challenges of their age gap, societal expectations, and the complexities of married life while Riko continues her education.

Riko is portrayed as cheerful, energetic, and deeply devoted to Naoya, often going to great lengths to fulfill her role as a wife despite her youth. Naoya, on the other hand, is more reserved and struggles with the moral and social implications of their relationship, frequently questioning whether he is doing the right thing. The narrative delves into their efforts to balance Riko’s school life with their domestic responsibilities, often leading to humorous and heartwarming situations.

Supporting characters include Riko’s classmates and teachers, who are unaware of her marital status, and Naoya’s coworkers, who occasionally become entangled in the couple’s antics. The series frequently highlights the contrast between Riko’s youthful exuberance and Naoya’s more mature demeanor, creating a dynamic that drives both comedic and emotional moments.

The plot progresses through episodic chapters, each focusing on different aspects of their relationship, such as Riko’s attempts to cook for Naoya, their efforts to keep their marriage a secret, and the occasional misunderstandings that arise from their unconventional situation. The series blends comedy, romance, and slice-of-life elements, offering a lighthearted yet thoughtful exploration of love and commitment across generational boundaries.