The girl he's in love with is coming over to his place, alone. Tagokoro Haruki decides on Saturday to prepare for this situation. Haruki is a virgin, as his raging boner in the morning can prove, and his step-sister — Tagokoro Anne — plots to fool around with his fluttering heart. This leads to him skipping his Saturday shift... During lunch time, his remarried step-mother — Tagokoro Madoka — plans on seducing him as a way to satisfy the itching inside her. She decides on doing that on that Saturday, when her husband is out of the house. Haruki's biggest struggle is to stay rational: to beast or not to beast? His Saturday had just begun.