While visiting my girlfriend's house, her older sister suddenly appears in the room, just out of the bath. She's completely naked, walking in as naturally as if it were her own room. Teasing me with a smile, she says, "Why are you so shy? We used to bathe together, remember?" Her body has matured beautifully over the years—her breasts are full, her pubic hair thick and well-grown, her nakedness radiating pure temptation. Unable to resist, I find myself helplessly drawn to her. Before I know it, I'm secretly pursuing a forbidden relationship with her, hiding everything from my girlfriend.