This prompt is the result of feeling yesterday’s prompt was a bit too serious and while this could definitely a rather serious situation it is also one that could be on the more absurd side. After all who would not consider a baby suddenly appearing without anyone being pregnant both serious and a little absurd.
Technically though, the prompt doesn’t say no one was ever pregnant with this baby.
This could be a science fiction setting where they have learned how to get someone’s egg and sperm without a person’s knowledge and someone else character this baby to term. This could be a fantasy setting where his father was the one who was pregnant, though it still would be a situation where the baby’s mother and father do not have much in common with each other. Have they even met? They certainly didn’t choose to have him.
His birth is certainly questionable, but what kind of person does he become. Does he have anything to do with his biological parents? Do they even know he exists? If they don’t how would they react if they ever find out?
You could play this idea as a comedy. Maybe his parents are thrust into the responsibility of parents when a newborn baby pops into existence right in front of their eyes. Maybe they were walking down the sidewalk and passed each other at some sort of magical crossroads and then suddenly they have a baby.
Or maybe it’s science fiction. It is common for doctors to take samples of their patients’ baby making pieces and everyone knows this. It is common knowledge that you might have a dozen children out there and just never even know it and everyone accepts this because it takes a village to raise a child right?
Horror or thriller is an option, too. Maybe his parents were kidnapped and forcibly made to give up the necessary building blocks to make a child because someone was obsessed with them and wanted a child with their specific genetics.
I’m sure there are ways to take this prompt and put it into other genres as well and I would very much be interested to know what take you went with and how you took this prompt and created the character in it and the world that brought him into existence.