I know I talked about this before with you guys but I have a decent idea to make it more interesting. On Earth it is the year 1974 and a series of strange events occur that are later dubbed Incursions. Strange individuals and creatures suddenly begin to appear across the world. People begin to develop magical and psionic powers. The Governments of the world begin to take action in response to these strange phenomena by developing new special ops divisions and new technologies.
The source of the Incursions are later discovered to be strange sights called Ley-lines that seem to be gateways to another world. However it turns out to be more than just one world. Some lead to a nightmarish realm known as The Warp, others lead to a strange reflection of Medieval/Renaissance era Earth, yet others lead to 8 magical realms where Gods do battle and much more worrying ley-lines lead to a grim alternate future locked in constant war!
Each place has strange parallels with one another. Fortunately the Warp's presence isn't as powerful on Earth as it is beyond the ley-lines. You are either a civilian or a soldier of one of Earth's countries who just so happened to get caught up in all this. You can join the Secret Service later on if you have the skill and the mettle for their assault teams or occult and psy-Ops.
Basically in layman's terms the ley-lines could lead to a Pre-End Times Warhammer World, Age of Sigmar and even 40k. But some unfortunately lead to the Warp. There are two magic-systems magic and psionics, magic is focused through the mind and psionics are focused through the soul. The job-system is where you either start as civilian or military and progress from there, you could even be recruited into the Secret Service. Chaos presence is weaker on your side due to it's slow spread there.
So Earth's relative safety and resources makes it Easy mode. Fantasy's lack of technology and constant danger makes it Medium mode. Age of Sigmar's huge domain and threats, plus lack of technology makes it Hard mode. 40k's Extensive span and insane danger level makes it Extreme Hard mode.