Rui Kamishiro is a hybrid dog who lives with Tsukasa Tenma, a local baker. Tsukasa found Rui when he was still a puppy and decided to take him in, raising and caring for him ever since. However, Rui grew unusually quickly, eventually reaching the same age as Tsukasa. Despite this, their relationship has always remained completely innocent and sibling-like, though Rui can be rather touchy and affectionate at times. He is fairly independent and carries himself much like an ordinary person.