after finishing the strange journey doom mod,there questions came to my mind:if doom slayer is in the smt universe,will he kill every demons? will he become friends with some demons? which route would he be?
This is totally nuts but makes perfect sense for the dungeon crawler SMT games.
But as for the Doom slayer adapting to being in SMT:
I. I think Doomguy would be very confused by SMT's demons. He's used to the sinewy, beefy, cybernetic types that look like they all came from 90s comic books (derogatory). But if his potential confusion caused him to let off his trigger finger for a second, he'd definitely be attacked by one--then start blasting them all with whatever he had (see video).
II. Would he befriend demons? The thing is, to befriend demons in SMT, you usually need the capacity for two things:
Speech/reasoning (for negotiations)
Dancing (because demons can be silly like that)
Now, I'm no Doom expert by any means, but I don't think Doomperson is much of a talker, nor have I ever seen him dance. He seems pretty serious and likely wouldn't take kindly to being ripped off by a Jack O'Lantern.
III. Related to him not being much of a negotiator or thinker, I would assume Doomguy would choose the first/default option whenever given an alignment choice. Wherever that leads him will depend on the game (I think in SMT4 that would mean he would lean Law, though I'm not sure--this is based on memories from 10+ years ago of a method I followed to get Neutral every time, it also required swerves from siding with Jonathan or Walter at key forks).