ok, got an idea: what about this: the scientists say to you he has a time maschine and if you want to try it, after that you are in a little route in ryouhi, ok? there is no way back because it's blocked so you have to move on, then 4 kids crash in you, say sorry and run forward, as you want to follow them the scientist put you back in present time.
before this we could include anywhere some people who told you about 4 trainers who become very famous in ryouhi, because they keep the region safe, that's because there was no crime here and ryouhi was always a region of piece.
well anyways: after you return to present, the scientists say he has to work on the maschine and say that you could come later and so we could activate the last "sidequests" after defending the elite4 or so on, but i think the event is kinda cool and it doesn't say anything about us or the ghost, so what do you think?
ah, and if we use the sidequests, what about only use places in jotho, so we could say that celebi (the pokemon of time) manipulate the maschine, so you go everytime there (of course every times diffent places) and catch rare pokemon and finally the legendary?
so what do you think?