One day, I, Momoka, suddenly collapsed and was admitted to hospital. Despite thorough testing, the cause is still unknown. However, since that day, I've been having these erotic dreams... That's right. And in the dreams, I'm always another person having sex with someone I don't know. It's basically like I'm having someone else's sex... Huh, today's dream is... my sister!? I've become my older sister...! Whoa, Yukina... Her boyfriend is doing all these perverted things... The things he's doing to her body... feel amazing...!! If Dr. Kaji were to find out about these dreams, he'd probably think I'm some slutty girl... What in the world should I do...!?