I've been wondering. What if Hiura has been prepping his asshole for anal, stretching it out for Midou on a daily basis. Even cleans up with an enema. But then. On the day they fuck, he forgets the most important thing. To empty his bowels beforehand.
So, after Midou finishes in him. He gets the feeling that he has to shit, and he can't hold it in. So, since his asshole is so loose after the fucking they did, he goes right there on the spot. Shit and cum just spewing out. And what if Midou still gets aroused by it and goes for a 2nd round after seeing Hiura's shit covered with his cum.
At least it wouldn't be as bad as a Chinzurena doujin. Where, sometimes, the one fucking eats a bit of the shit. Yeah. Honestly, y'all should look up Chinzurena doujins to get used to the worse non gore aspects of trap doujins.
Depending on your tastes. We also have anal prolapse as an option. Just Midou fucking Hiura so hard that instead of leaving him gaping, he pulls out his asshole.