A university research lab serves as the setting for this story, where graduate student Satoshi Onozuka has a reputation for being so absorbed in his work that he routinely forgets to eat and sleep. His junior, Izumi Hirasaka, a composed and practical senior undergraduate student, has assumed the unofficial role of Satoshi s caretaker, earning him the label of Satoshi s owner from their professor and peers. Izumi brings Satoshi food, ensures he goes home, and manages the daily tasks that the scatterbrained Satoshi cannot handle on his own. Satoshi is generally innocent and oblivious, coming from a family that owns a traditional inn, which occasionally surfaces as a greedy streak, while Izumi is a natural caretaker with bleached blond hair that belies his serious nature.

The central conflict ignites when Izumi discovers that someone has assaulted Satoshi. The realization that another person touched Satoshi without consent triggers a powerful shift in Izumi, transforming his simple desire to protect into a much more intense and possessive romantic obsession. No longer content to simply be a caretaker, Izumi begins to see Satoshi as someone he wants to claim exclusively for himself. The story follows the evolution of their relationship from a pet and owner dynamic into a romantic partnership, though Izumi s management habit proves difficult to shake. As they navigate this new phase, Izumi struggles to balance his natural urge to control and manage every aspect of Satoshi s life with the need to respect his autonomy as a boyfriend.

The main characters are Satoshi Onozuka, a pure-hearted but helpless researcher who is prone to falling asleep while waiting for instant noodles and who credits Izumi for his survival. Izumi Hirasaka is the younger boyfriend, a possessive and caring young man who is often referred to as the keeper. Supporting characters include Professor西島, who has an animal instinct for detecting feelings and quietly encourages the relationship; a guest professor named Takao Yasuo who takes an interest in Satoshi; and various other students and family members who populate their world.

Notable narrative arcs include the initial awakening of Izumi s jealousy and desire following the assault on Satoshi, leading to their first confessions. A significant arc involves Izumi trying to suppress his overbearing caretaking habits as their relationship becomes more serious, believing that he needs to give Satoshi space. However, when a high school student with a particular taste for people who are already taken shows an interest in Satoshi, Izumi finds his possessiveness surging out of control. Another arc involves Satoshi getting into a troubling situation with the guest professor, forcing Izumi to confront the limits of his role. The story also includes spin-off narratives focused on side characters and their own complicated relationships.