I mistaken my sleeping sister-in-law's butt for my wife's butt, and immediately inserted it without knowing that she was her sister-in-law.

Shinji makes up and has sex with his wife, who is fighting over trivial matters and is sleeping. She rubs her plump, meaty butt and cums inside her in a thrust. I was so careful that it felt better than usual that I forced her to kiss me... and the person I was there was, I was surprised, my wife's sister! "S-Sorry, sister-in-law!" His sister-in-law forgives Shinji as he groans and apologizes, but he can't hold back his body, which is beginning to ache.