Mai Fuyuki, 44 years old. Having lived solely for her work while her husband remained distant, she gradually finds her heart drawn to her kind and warm son. Before realizing it, she begins seeing him not just as family, but as a man, harboring forbidden desires she cannot suppress. Today, the two of them are alone on a hot spring trip. Staying at a mixed-gender onsen inn, she fears she may no longer be able to control her feelings for her son.