I don't know what caught me off guard most.
1. A Demon King played straight (for now)
2. Modern day Earth exists and this isn't the standard isekai stuff we usually get (again, for now); or
3. That Maou-sama got sent to Mars of all places.
Wouldn't surprise me if a government tried to claim that the walking and talking human-like thing was just a dust storm and some weird light reflections.