Satsuki and Yayoi decide to visit their brother Hazuki, who is studying in the realm of Ulster. While following a stray cat, Satsuki stumbles upon a mysterious mansion. There, he will meet the owner, a fascinating hikikomori with an attitude, and the beautiful, friendly butler. After a series of circumstances, the brothers end up running up debt after debt, and they'll be forced to work at the mansion until they can pay them off!