I've heard and read proofs that writing fictional stories are haram. Some people, like me, are given talents of writing poems and stories and the like. I've made up a story that is really beneficial and I've always dreamed of sharing this with people, but the main character was born with strange powers (growing claws and teleporting, i.e. moving from place to place in a second.) The story goes on about how he is trying to live despite the people who are chasing after him to end him. Is it haram if I write something like this? If it is haram, can I make him inherit the power by one of his ancestors who was injected by an undiscovered drug?
As a muslim, I have never been told, heard or read in any hadith that writing fiction is haram, so take my words with a grain of salt and make sure to ask around! it's after all based on my experience. The only precaution I was ever given was to not write/promote or read any texts that are blasphemous to Islam, Allah(swt) and the prophets(pbut), including things such as "الغيب" and adjacent topics.
In general, I think it's no trouble to right anything in fiction so long as it doesn't directly transgress the Islamic perspective(i.e: writing a story that humanizes god, etc...). After all this story is your product, and it's definitely your creative freedom to write about controversial moral dilemmas and whatever you like, but conditionally; say your interested in making a drama, a woman that two-timed her husband, writing the story isn't haram per se, if you later decide to add a description of an explicit sexual intercourse...then I think we have a problem! But the problem isn't the two-timing, the lies and whatever the woman is doing, it's simply how you choose to pen it.
In the case of supernatural stories, the question becomes a bit tricky, but the premise remains intact. Though I would keep the world my character has outside the contact of "الغيب", Allah(swt) or anything pertaining to Islam in general, I don't find it necessary for your character to be muslim or associated with Islam. If I were you, I would either nullify the religious or spiritual facet of my character altogether or just occasionally mention it.
By writing you're conveying a moral lesson, so make sure you're sending the right one, in an appropriate fashion :) Hope this helped!
P.S: Check out some Zakir Naik or other sheikh's videos in youtube.