It all started with the end of the world. Seriously, the Biblical Apocalypse actually happened much to everyone's surprise. The Rapture of the Faithful, the Spread of Darkness, the Four Horsemen, the Anti-Christ, the Rise of the Armies of Good and Evil - all of it. The only part they really got wrong was how it ended. It was supposed to be the War to end all Wars with Satan finally defeated and God ruling a perfect paradise forever.
Instead, we got a few war stories then life went on. The armies of Heaven and Hell expected us to chose sides and fight with them - but instead we chose our own path. Even the "Good" guys decided that they wanted to kill everyone, so in the end we decided to give a big "screw you" to them both.
Funny thing though. Turns out, both the armies of Heaven and Hell apparently had made no big changes in their military hardware or strategy since the Roman Empire. So when Humans entered the final battle of Armageddon we brought modern technology and tactics - and as a result the war was so one-sided it made jokes on late night television. Oh sure, and individual demon soldier or heavenly angel can take a human - but since when do humans fight alone? It was nicknamed the Curb Stomp War, and instead of ending the world it became just another skirmish.
The surviving members of the forces of Heaven and Hell gave unconditional surrenders, and in return we proved to not be total bastards. The surviving supernatural creatures of the world were for the most part allowed to live among us, if now they had to register with local immigration authorities and were now subject to human laws. In America, this meant that NIS gained a new branch called the SINS, the Supernatural Immigration and Naturalization Service. Excuse the name, with the Rapture taking away all the Bible Thumpers we're a little more relaxed about a little blasphemy between friends.
It's not a bad gig if you can get it. It's a lot like a normal immigration agency, but since the clients this time are a bit stranger by law and pretty rare it's not unusual to only need a few social workers and even then they only have 2 or 3 clients each.
"Nick Brooklyn" is a special case that gets special attention though. A registered Demon trying to make a living in NYC as a writer but he's famous for something else. Supernatural creatures usually reproduce via complex rituals and magical ceremonies. Most of them are even genderless. But "Nick" is an Incubus, a demon that specializes in sexual sins. So he not only actually is naturally male but he can father offspring the old-fashioned way, and actually can in theory father children with any female sentient being.
Which makes things interesting for sure...
So a world where the supernatural exists, is out of the bag, and the creatures are subject to human laws now. I'm picturing my character is a legally registered demon whose recently been outed as an Incubus, one of the few supernatural creatures that can reproduce without complex magical rules and regulations - he can just knock females up like any other frat guy. As a result he gets more attention from SINS then most. Your character is his social worker, trying to keep him out of trouble. That's just what I'm picturing though, we can discuss that. You can kind of think of this as a sex-reversed and slightly less comedic version of Ugly Americans if it helps.