@Brutu How can you be so cruel and mention it without at least giving the title... Ah this cruel world.
@OP_Zed If you want STIs/STDs you have to take other diseases and plagues as well. And where does using logic for this kind of manga gets you? In quite possibly 2 disease & plagues ruined world where isekai'd people export our pathogens in their world , and since they came back, their pathogens to ours. Don't go there and just forget STIs are a thingwhile you are reading this.
And who says magic doesn't cure it all anyway as well as work as contraceptive? Maybe we should be scared of getting their STIs/STDs since we have no magic and have to rely on science. Does pathogens that infest slimes, monsters, demons and other otherworldly species can even cross to humans? They cross from animals to us because we cohabitate but humans and all those mentioned about don't cohabitate but kill each other so there are way less chances of pathogen crossing on different species. And if you want to go further in details, there are more cans of logical worms to open. Do I want to read about it? Yes, it seems like fun to me. But should someone research and write and draw manga about it? Yes. Can't assure them they'll earn a living but hey, sound like fun manga full of death and pain. Is this manga like that? No so keep your brain off and logic on the leash while reading it.