Depends on which story.
Divine and Conquer: If isekai'd here, then they will get magic and have a decent chance of surviving. However, if they're above 15 and don't have a psychic to unlock their magic, they will literally explode. Also if they're transported to the main country the story takes place in, then they'll have to be forced to live with a government where the military controls everything, big businesses can sell their stuff for massive profit cause they essentially bribe the government, and good luck trying to live the literal apocalypse if a god gets angry.
Heroes and Villains: Probably might make a decent living, though they'd live in poverty and disease. Considering most of the major countries are controlled by duchebags that can barely function on a good day, they'll have to fight for a scrap to live. Don't even get me started on the regular fights between the hero and evil magic users that could potentially control the world and heaven's involvement with the oppression of the dead.
Tower of Redemption: Depends on the floor. If they're born in floor 50, dead in like 10 seconds. The floor is crime-ridden and the gangs control the government. If born on a higher floor, then they might have a chance, though there's deadly monsters and systems on each floor. Like the legal child experimentation.
My Succubus Roommate: If they live in the main world, it'd be basically living in our world since the story is based within our world. However, if they're isekai'd to the Succubi continent, I give them 10 seconds tops. Considering how much of a hellhole I made that place, I doubt anyone could live there for long without get arms and genitals cut off.
Call of the Dragons: I give them a month before they die. I can't really explain why because of the amount of ways I put in this story that could kill a person, but it can range from minor poisoning all the way to slow torture as someone rips the soul out of their body.
Parallel Doomsday: Good luck surviving here for even a second. Considering the main antagonist of this story is a universe destroying apocalypse, I highly doubt they'll live.
