Sae divorced her husband and lived with her son. My son didn't have a girlfriend, he didn't go out on holidays, he just slept all day. Sometimes, I invited him to go on a hot spring trip just so the two of us could take him out. A son who always loved his mother... Sae was confused by his sudden confession, but he gave in to his son's enthusiasm and opened the forbidden door with the promise "If only once...". It was just a one-time promise, but in the end, the surge of pleasure awakened Sae's female instincts...