The Masquerade has ended. All the cryptids, beasties and things that go bump in the night have come forward--and are now part of everyday life. Centaurs share the bike lanes with demons, Satyrs run kicking night clubs, vampires work night shifts--and people react to these things, like how you react to a new Starbucks opening up.
At the same time, the night sky is alight, as it turns out humans have already been to space and made first contact. The humans on Earth--what we consider modern day Earth--were the ones who were left behind for "not being advanced enough". With several space faring nations existing... and causing different strange effects that affect Monster Earth.
Most of the action ends up being Seinfeld--but with demons, slimes and monsters.