Sumire was invited to a hot spring trip by her son. She couldn't help but be happy, as she had never been to a hot spring since she married her husband, who hates hot springs. After arriving at a nice-looking inn, the two immediately head to the hot spring. Sumire was enjoying the open-air bath in the refreshing sunlight. A shadow sneaks in and peeks at her. Her son was peeking at Sumire bathing. That night, the son gives his mother a massage to soothe her. Every time he touches his mother's body, his son is about to burst with his secret feelings. Late at night, the mother is quietly breathing in her sleep. The son has reached his limit of patience, so he gently lifts the futon and begins to play with his mother's body, which is visible through her yukata. The mother opens her eyes, feeling something strange about her body. Surprised, she tells her son to stop, but Sumire is forced to kiss him. When her son tells her that he likes her as a woman and asks if she has to hold back forever, Sumire can't help but love her son and offers her body to him, saying that he can do whatever he wants...