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