Not sure if okay to ask, if this is offending or so, please let me know and I'll delete. 

I used to have this friend of mine. 
He was hands down obsessed with Snow Villiers from Final Fantasy XIII, coincidentally he had some resemblance to the character.
He took it upon himself to sort of become the character, to look more like him, to say things Snow did, in general have these overly "epic" fantasy manners. One thing he especially clung unto was the whole hero-aspect he saw in Snow.
It was obvious he was trying to legit be the character, but he would try to portray it as "see how weird this is? It's like this game studio made this character based off of me? What a coincidence! I just HAPPEN to love this series guise."

There were a couple of other characters as well, that he didn't go quite notoriously all-in with. He did try to "merge himself" with the characters if that makes sense, but never was as vocal with them as he was with Snow.
Both were video game characters too, Snake from MGS series, and Dante from DMC series.

I figured this behaviour would be (mostly) unique to him, but then I've come across other such instances online. Most notorious being the story of the "Final Fantasy house", where lived together three individuals all interested in Final Fantasy 7. Two of them actually thought themselves to be these two characters from the game.
Other cases I've seen are usually random people on social media, the common theme seems to be epic video games and edgy anime.

I've been wondering, is this some sort of mental condition perhaps, some sort of identity thing? Some of the cases I've seen are merely roleplaying gone a bit too far, but then there are the extreme cases that some can be a bit disturbing.