Mizuki has just lost his job. Without money or a place to live, Mizuki has no choice but to stay with his older brother in his company dorm room. Since non-employees are not allowed in the dorm, Mizuki must live there in secret, like a house cat. At first Mizuki is intimidated by his older brother's roommate, Toru, but seeing a softer side of Toru changes his opinion. Toru starts to treat Mizuki with kindness, but Mizuki wants to become more than just a pet companion.