Haru Aiba, the young heir son of the long-established hot spring inn: Aiba-en.

At a young age, he was obsessed with it, peeking at his mother's "that act." His mother, transforming from a mother to a female in heat, always surrendered herself to pleasure and let out coquettish cries. The head maid of the inn, or the father who occasionally returns home. The daytime faces and nighttime faces shown by the adults affect young Haru's heart and body...