Sae divorced her husband and lived with her son. My son doesn't have a girlfriend, he doesn't go out on holidays, he just sleeps all day. Sometimes, I invite him to go on a hot spring trip just so the two of us can take him out. A son who always loves 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...