Because of work, Mitsuru has moved to Tokyo and lived alone for three years. During a medical check-up, he found out that he had a tumor. Thinking that he didn't have much time left, he took his beloved mother on a trip to enjoy some happy days before he died. They stayed at a hot spring hotel together. Mitsuru had secretly loved his mother for a long time. So when his mother got drunk and accidentally revealed her beautiful underwear in front of him, he couldn't resist touching and exploring her body. His mother woke up and stopped him, so Mitsuru told her about his limited time left. Out of love for her son and wanting him to fight against his illness, Aoi agreed. When they returned, Mitsuru went for another check-up. It turned out to be a benign tumor, but due to the seriousness of the doctor's expression, Mitsuru misunderstood. After this incident, the bond between the mother and son grew stronger. Even though there was no longer a threat to life, Aoi still agreed to have a relationship with Mitsuru, even though she knew it was wrong...