Due to work, Mitsuru has been living alone in Tokyo for three years. During a medical check-up, he discovered a tumor in his body. Thinking that he may not have much time left to live, he decided to take his beloved mother on a trip to enjoy the remaining happy days before his death. They went to a hot spring hotel together. Mitsuru has secretly loved his mother for a long time. So when his mother got drunk and revealed her beautiful underwear in front of him, he couldn't resist exploring her body. His mother woke up and stopped him, Mitsuru then revealed his limited life expectancy to her. 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, and he misunderstood due to the serious expression of the doctor. After this incident, the bond between mother and son grew stronger. Even though his life was no longer in danger, Aoi still agreed to have a sexual relationship with Mitsuru, knowing that it was morally wrong...