It's not like there is any universally accepted definition of the word waifu, so I suggest simply calling her whatever you want and ignoring the people trying to "correct" you.

There are people here with waifus from western fiction. I haven't seen them run into any issues with the term.

You were kind of vague about what you meant by non-anime fictional character, so I'd personally break it down like this in terms of examples.

Katara - Perfectly fine.
Starfire - Perfectly fine.
Wonder Woman - Some people might find you weird but she fits the 2D mold so I wouldn't worry as long as you don't post stills from live action movies.
Hermoine Granger - Never bring up or post pictures of Emma Watson, otherwise you're fine imo but people may argue with you.
Dana Scully - It'd probably be wise if you don't mention who your "waifu" is and definitely don't post pictures of her.

Despite what I said I think it's fine to refer to her however you wish in your head.

>>13302
Love who you want love is love but /mai/ itself is more for anime characters really, I guess there could be exceptions I dunno but it's going to get too complicated if we start doing that in my opinion.

>>13306
I don't know who the first two are, but what about a character from a 3D CG movie?

>>13537
You mean like Disney or Dreamworks stuff? That'd be very, very atypical but I guess I could live with it. As long as it's a fully fictional character that exists sololy in art/media, I'd say is in the spirit of 2D love.

>>13540
I meant a character from a movie with japanese origin, such as Final Fantasy VII:AC or The Spirits Within.

>>13541
I see no problem with it.

>>13541
Go for it, I have no issues either.

>>13302
there used to be a guy here a year or two ago who's waifu was Raven from Teen Titans. I don't see a problem with it.

>thin air kissable

This sounds like a cute term to use