You're the submissive pet to a very fat, very dominant gainer. After a massive meal, he demands you rub his belly to help make room for his next feast. All the while, he praises you for being such a good pet, and he even comments on how you're starting to plump up a bit, too. You can't help but get excited hearing all his praise and rubbing all his fat, so you end up grinding against your master's belly to get off.
This audio opens with a very loud burp and includes more burping sounds throughout.
I posted a written fic a lil' while back about a dom gainer with a feedee pet, and this is the same character in the same universe. Both pieces were inspired by the user Chubote on Tumblr, if you'd like an additional visual of what you'll be rubbing up against.