(Note: the game is free now, there's just some conflicting info that hasn't been updated, you can download the premium version for free.)

It's kind of a little sex sim thing. You have sex with the Slugcats from Rain World.
Overall it's kinda basic, really ALL you do is just have sex with them, with not much variation. There's a couple cosmetics, you can pick the slugcat (basically just the color) that you like, and what you're sticking into them (dicks or objects), and there's achievements to unlock too, in the "paid" version. (One cosmetic is huge boobs.)

Something of note: the game's currency is cum, so what you do is you fuck her and cumflate her, then when you want to "cash out" and get your money to spend, you simply pull your dick out and let her deflate.
The max size covers the whole screen with her belly, so, uh, have fun, heh.

Overall it's not bad, just unpolished.