>What do you think of the other characters based off this porn alone?
Dipper seems pretty chill. He's probably a straight man foil when with other, zanier characters but a chaos agent when the scene calls for it. I'm guessing he's the main character in the cartoon. My guess from the way he's portrayed here is that he's got a straight-laced streak that other characters tease him for.
I feel like Mabel could be tooth-grindingly annoying in the wrong hands but here her kUhrAyZeE streak lends her an endearing spontaneity. There's a little bit of too-overt childishness to her that rubs me the wrong way but it's balanced out. But it does give the sex a refreshing and tension-free feeling like >>1834
says, and without that little extra levity to thin it out this porn comic could easily get clotted. My guess is that she fills a similar function in the cartoon.
Wendy's portrayed here as an old flame/crush of Dipper's. I read her as a straightforward tomboy. My guess is that she fills the role of semi-main satellite character/counter-foil in the cartoon, and probably teases Dipper or otherwise throws him off-balance. The friendship with Mabel would make sense under those circumstances.
Mabel seems annoyed by Dipper hiding his relationship, but I only just noticed on re-reading that she's more annoyed on Paz's behalf, which I find very sweet.