High school student Umi Sayama views her life as a monotonous routine, but her ordinary days take an unexpected turn when her mother departs on a lengthy business trip. Umi is entrusted to the care of their neighbors, the Hiroi family, and must temporarily move in with them. She harbors a secret excitement about the arrangement because the Hiroi household is home to Shouya, a young man eight years her senior whom she has admired since childhood. She eagerly anticipates a heartwarming reunion with the kind, diligent honor student she remembers from her past.

However, the Shouya she encounters is almost unrecognizable. The former model student has undergone a drastic transformation; the person now living next door is a messy, unmotivated young adult who seems far removed from the idealized figure in Umi's memories. In a shocking twist, Umi discovers that the slovenly Shouya now earns a living by drawing adult manga, working as a hentai mangaka. This revelation shatters her nostalgic image of him and forces her to reconcile her long-held feelings with the reality of who he has become.

The story follows Umi as she navigates this awkward and surprising cohabitation, learning to see her childhood hero for who he truly is. The manga blends romantic comedy with a significant age-gap dynamic, exploring how Umi decides to move forward as her initial admiration collides with Shouya's unconventional career and slacker lifestyle. As the first original serialization by Daisuke Hagiwara, the artist known for Horimiya, the narrative focuses on this faintly sparkling cohabitation and the journey of meeting changed memories once more.