When Saku took in a stray black cat, she never expected that he would become the equivalent of a housekeeping life partner. But Yukichi, a giant cat who towers over Saku, is not your ordinary feline. He takes great pride in his culinary skills, and a good sale at the supermarket always gets his whiskers twitching. Saku may not have her act together yet, but at least she has Yukichi!

Uesugi Ren and his sister Mihato ran away from home because of domestic violence. When they at last reach the city they have a hard time finding work to earn some money. They eventually enter the service of the Kuonji family, making a pledge of absolute loyalty. Thus Ren's days of being a butler to the demanding Kuonji heir begins...