That is perfect for Necromunda

The 40k fluff explained to an outsider:
Some space elves got really into drugs and sex and a big scary monster got born that ate them.
A space wizard got beaten up by a guy who said he was his friend but wasn't and now he's on a life support machine and people worship him because he was super awesome.
Now there are giant men with rocket launcher machine guns and 4 hearts and are really super awesome who beat up everything.
Also there's a bunch of aliens but they don't really do anything and aren't as cool as the rocket machine gun super men, so who cares?