Ryota is living alone for the first time in a long time after his wife returns to her hometown to give birth. Feeling lonely in his empty room, Ryota warmly welcomes his sister-in-law Reina, who suddenly shows up. However, Reina's real purpose is to have an affair. Ryota is enjoying a carefree bath when the evil hand creeps up on him, unaware of this. Reina smiles at his beautiful face, and her plump, lustrous body sways and blows away his reason...