It's summer vacation, and the Nanase family's parents have left the country on a trip. Our protagonist and his five younger sisters remain behind to spend the break on their own, but...
Free from the constraints of school or parental supervision, the sisters have been making odd advances toward their brother, leading to a series of sensual events. Faced with all this, the brother can hardly contain his arousal.

Just how far will the Nanase siblings go?