Ami Nonomura, who lives with her aunt, moves in with her half-brother Hiroshi to care for him. Hiroshi has lost his mental balance since the death of his real sister, Mami. Under Ami's diligent care, Hiroshi gradually recovers. However, conversely, Ami begins to be plagued by erotic nightmares. Ami learns that Mami's death was a suicide, and that the cause was her pregnancy resulting from a forbidden love affair with her brother Hiroshi. Hiroshi's heart was still trapped by Mami. Ami makes a decision. "From today, I'll belong only to you, big brother. So please, forget about Mami..."