As I'm informed by a short lookup, a sharingan is a skill from the Naruto franchise. Consequently, a sharingan user would be a fictional character, and consequently a person identifying as such character would be a fictionkin. Naruto does certainly qualify as fiction, but not myth in my opinion. The only exception would be if the sharingan would also have been described in asian mythology, but it doesn't seem to be the case.
Another note: since you mentioned obtaining a sharingan.. if you refer to obtain the actual skill (as opposed to e.g. an item which would represent it), please note that it's not possible to obtain a fictional skill in this world. It wouldn't be called fictional otherwise :biggrinderg:
If I remember right from the stuff I saw on wattpad, mythical refers to real life "mythical creatures" like physical werewolves, vampires, and the like, correct?
If yes, no it won't make you a "mythical". Physical shifting is not possible. Especially not through subliminals, I'm no sure why people think they can make you grow wings or become a werefox. You will not get red eyes with black dots and the capacity to copy people's every move.
I personally recommend martial arts and studying body language if you want to achieve a similar skill though! It's probably what closest ressemble it.