Based on the erotic game by Moonstone Cherry. With their parents departing on a business trip, Yuuichi was left alone with his five imoutos for the entire summer vacation. He wanted to take advantage of this opportunity to be closer to his imoutos, and they were also strangely assertive, leading to ecchi incidents one after another. Just how far will the Nanase siblings go? (Source: Hau~ Omochikaeri!)