Honestly a lot of it comes down to you searching for what fits what you like on sites like this and itch even if it means you have to slog through lots of games. Even with that most of them will just be maybe a character or two that fit your definition unless you focus on games that involve gaining like spectrum of hybrids does with some of it or vore type stuff which neither are all that common. Honestly most of the games said so far are your best bet, though linking an image or two of exactly the type you are looking for might help as well.
Roads Yet Traveled has a couple characters that might fit it but it's still ongoing, along with
Shelter having one too.
Hearthfire and
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have larger guys.
Santa Lucia,
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,
After Class,
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(Monster Hunter) have a character or two with a belly.
Killigan's Treasure has you playing as a bull with a belly and might have romance options and the like later on that have one.
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is mostly muscle stuff, but there might situations later down the line that fit.
Worshippers of the Gain and
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if you don't mind weight gain stuff.
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and
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if you don't mind vore.
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is gonna have a lot of kinks so it might have something you like now or down the line.
Sihai's Legacy has a lot of chubby guys.
