Kobeni Yonomori, a high school student, lives a relatively ordinary life until her 16th birthday, when she learns she has been engaged since childhood to Hakuya Mitsumine, a boy she has never met. Hakuya and his younger sister, Mashiro, move into Kobeni’s home to live with her family as part of the arrangement. Kobeni struggles to adjust to the sudden changes, particularly as Hakuya is quiet, reserved, and often difficult to read, while Mashiro is energetic, clingy, and deeply attached to her brother.

As Kobeni navigates her new living situation, she discovers that Hakuya and Mashiro are not entirely ordinary. Mashiro possesses supernatural strength and agility, and Hakuya exhibits mysterious abilities, hinting at a hidden background. Kobeni’s older sister, Benio, who is fiercely protective of her, initially opposes the engagement but gradually warms to Hakuya and Mashiro. The series explores the dynamics between the characters as they grow closer, with Kobeni slowly developing feelings for Hakuya despite her initial confusion and reluctance.

The narrative balances slice-of-life comedy with light supernatural elements, focusing on the everyday interactions and growing relationships within the household. Kobeni’s school life also plays a significant role, as she interacts with her friends, including the cheerful and supportive Niko, and deals with the occasional misunderstandings caused by her unusual family situation. The series maintains a lighthearted tone, with moments of humor and warmth, while subtly addressing themes of family, trust, and the challenges of adapting to unexpected changes. The characters’ personalities and relationships drive the story, creating a blend of comedy, romance, and mild intrigue as Kobeni and Hakuya’s engagement evolves into a genuine connection.