"Oku-sama wa Joshi Kōsei" centers on the unconventional relationship between Naoya, a 26-year-old office worker, and Saki, a 17-year-old high school student. The two meet when Naoya moves into a new apartment and discovers that Saki, his neighbor, is his arranged fiancée, a decision made by their families without their prior consent. Despite the initial awkwardness and societal challenges, the two gradually navigate their relationship, balancing Saki’s high school life and Naoya’s professional responsibilities.

Saki is portrayed as a diligent and mature student who takes her role as a fiancée seriously, often going out of her way to support Naoya. Naoya, on the other hand, is initially hesitant about the arrangement but grows to appreciate Saki’s dedication and kindness. The series explores their daily interactions, blending moments of lighthearted humor with the complexities of their situation. Saki’s classmates occasionally become involved, adding layers of tension and misunderstanding, particularly when they misinterpret the nature of her relationship with Naoya.

The narrative delves into themes of responsibility, societal expectations, and the challenges of maintaining a relationship under unusual circumstances. While the premise is rooted in the unusual arrangement, the focus remains on the evolving dynamic between Naoya and Saki as they work to build trust and understanding. The series balances comedic elements with heartfelt moments, offering a mix of slice-of-life and romantic drama. The characters’ growth and their efforts to reconcile their feelings with external pressures form the core of the story.