[quote=@harinezumikouken]
<Snipped quote by Guess Who>

No, what I mean is if their future self warps to the 'past' or being to present for us.

And say they happen to 'kill' their past selves.

Wouldn't that create a time paradox?

What I'm asking is, if it'd be acceptable or make more sense if our characters' evil selves can be from AUs instead of future timelines.
[/quote]

Ah, okay. Any reason for why the evil doppelganger exists is acceptable as long as it makes sense for the story, so future Shiro going back in time to kill past Shiro is acceptable as long as there's an explanation as to how he traveled back and why he would want to break all of the space-time continuum.