
Yes they do, the anal cavity isn’t a vagina. Semen gets absorbed in woman hooha but not in a persons booty hole. It sits there and causes havoc because the lining isn’t meant to absorb jizz. Plus it’s messy. And have you ever heard of a poo noodle? Poop can get stuck in a guys urethra so when he pees a noodle of poop comes out. It’s nasty as hell to see that up close. And have you seen jizz shoot out of an unclean butt and make a mess? Use a condom.

Btw semen doesn't get absorbed in the vagina. It gets destroyed. The vagina is very acidic by nature, so it breaks down the sperm that gets introduced to it. That's why a man is considered infertile if he has slow sperm, cause it would het destroyed before it reached the egg to fertilize (if there was one).
The anus/rectum doesn't have suck factory settings so it's more difficult to deal with

They're taking advantage of the fact that it's fiction ig. Usually, if testing is brought up, it'd give the impression that it's part of a "conflict"(?) that'll appear in the story, so maybe that's why?
There's a chinese novel "the stars around the sun" it's called, i think, that brought up testing quite a bit (through a movie though). It has a manhua too iirc, though idk if it lived up to the novel (art is good tho).
I have seen this often in other manhwas, where protagonists will refuse to sleep with each other without protection. I wonder why, because if they’re both clean, it shouldn’t be an issue (in other stories one person will even get up in the middle of the night to buy condoms)