Her mother, Yumi, who lives with her husband and son, Seiya, has a secret. She loves her only son, Seiya, so much that she wanted to get rid of her worldly desires, so she was hiding from her husband and performing her sexual processing. However, her obscene behavior, which she thought was good for her mother, had greatly expanded her son's hidden desires. Seiya wanted to have sex with his mother, and he couldn't control his desire. When Yumi reflected on her own actions, she could not resist Seiya's demands, and finally crossed her forbidden line.
