After getting divorced, she took in the younger of her two sons and raised them. When her ex-husband passed away, the three of them reunited. They were planning to go on a trip together, but the younger brother couldn't make it, so it was just the two of them, the older brother. In fact, after not seeing each other for many years, the older brother began to think of his mother as a woman... He's always loved his mother... He can't hold back anymore. Chisato refuses at first, but her brother's strong enthusiasm leads her to give in, saying, just once. The intense pleasure won't end with just one time... A new relationship between parent and child indulging in forbidden pleasure begins now.