Bringing her boyfriend home was a bold decision for the younger sister, even though she knew that her older sister, Hatsukawa, was famous for being a charming woman with eyes that captivated boys. Her younger sister's boyfriend is no exception. With his sexy and proactive sexual actions, he is easily fascinated by her. Even though they knew it was wrong, sneaking around behind their poor sister's back made both of them feel happy because it gave them a mysterious and new feeling. But in the end, the most pitiful thing is still the younger sister who was cheated on by her boyfriend but still seemed happy, not knowing the bad things that were happening to her.