A mother named Yukari has raised her son alone since he was young, and now that he's found employment, she feels an overwhelming sense of accomplishment. Four years ago, they made a promise to have sex just once... ever since then, her heart and body have ached with longing. When her son invites her on a hot spring trip out of gratitude, she accepts eagerly despite knowing their past cannot be forgotten or forgiven. As they embark on this forbidden journey together, a new taboo relationship begins to blossom between mother and son... This is a story about incest!