Hiya! For a prototype and your first game here, this is really good! Yasa-chan is very cute <3.
But I don't think she farts enough. Yasa needs to be gassy, really gassy. I hope you add a lot of variety in the kinds of farts she can rip, it's an aspect of fart fetish that I don't think games have taken advantage of, that being the wide variety of properties in flatulence. Loud, silent, airy, wet, etc. A lot of Yasa's toots sound wet and sloppy, nothing wrong with that not at all, but I don't think Yasa's butt should always sound like there's a full septic tanks worth of poop waiting to spew out her backdoor.
It would also ne nice to see variation of the fart graphic too. Heavier farts should have thicker fumes and sharp farts should look like a jet of gas coming out of her butthole. Stuff like that. Different color too. Maybe the farts go from green to yellow/orange to brown depending on how much poop in in her bowels or from what she has eaten. Maybe a slight red tint for hot and spicy farts.
If you're down to do an internal view of her bowels that would be sweet but I won't lose sleep over it if you choose not to.
I hope you make this the best it can be! <3 <3 <3