The only thing I can think of that hasnt been mentioned is possibly Akira. It would be a pretty difficult world to use in more than passing unless setup with a similar cyberpunk plot (like bubble gum crissis) or an armageddon type event.
I have to agree though that Rune Soldier isnt used as much as it could be. It would be especially easy to cross into a slayers setting or something similar as the anime covers very little outside of Ohfun and the surrounding territory (making it an ideal candidate to be dropped on the map somewhere). It brings to mind an excellent story I read on fanfic.net called Rune Soldier Ranma. Had a lot of creative additions that fit the feel of both series. It probably wouldnt take much to place Ohfun on a silver millenium era earth. Of course short of back story purposes some kind of time travel plot device or situation would probably have to be used to make the effort worth more than a reader's easter egg.







