Part 1 and Part 2 are here.

After a few days of this I worked up the nerve to ask my girlfriend if she would possess her mom for some fun. I'd only met her mom a few times and they were all memorable for the wrong reasons. She was a hard woman to like, sour and mean but with a tremendous rack. I thought my girlfriend might balk at this but her relationship with her mom was just as charged as mine and she readily agreed."Meet me at my mom's place in half an hour," she said, before disappearing.Exactly 30 minutes later I rang the doorbell and was greeted by my girlfriend's mom wearing nothing but a robe. She pulled me back into her bedroom and we had her way with her mom on her own bed. Part of the fun was spite fucking this woman who'd been so awful to me. Pounding her wet pussy as she moaned. My girlfriend kept asking for more humiliation: spanking, hitting, spitting. She got off on abusing her mom's body as much as I did.I shoved my dick between her massive tits and tit-fucked her as fast as I could. I grunted as her breasts bobbed, my cock disappearing at the bottom of her cleavage and reappearing at the top near her lips.When I was ready she sat up and I came on her face, pumping my hot seed and watching it splatter down her mom's chin and drip onto her breasts. I coated her with my seed and my girlfriend made her mom bathe in it, rubbing it all over her body until she was filthy with my cum.I barely got out of the house before my girlfriend returned to her own body. I could hear her mom screaming from out in the street.

A car accident leaves a dropout brother swapped into his perfect sister's body in Moving On, available on Smashwords, Amazon and Body Swap Stories. Preview here.
https://bodyswapfiction.com/enter/?p=11362