(last updated: 12/28/17)
The monstrous denizens of the dark are faced with many challenges, mostly because there are so few of them. While there are numerous references to the 'demon world' in Darkstalkers' source, in the world as we know it, this is merely and mostly a colloquialism for monstrous subculture. The actual demon world resides somewhere in the leylines, away from free access by most.
As the playable Darkstalkers have all been created on game, adapting them to the theme is not very hard. The key factor to keep in mind when playing a Darkstalker is that they are exceedingly rare. The number of monstrous people in the world is a subset of the number of fighters, which is itself an extremely small subset of the entire world. A lower ratio and less informed Darkstalker is likely only going to have seen maybe one or two other creatures in the world in their entire lives resembling them. Feeling isolated and being treated as a bit of an aberration at best is normal for the monstrous.
Several characters are not allowed from the game Darkstalkers. PYRON is an immensely powerful alien made of fire, and as such is unthemely. HUITZIL, because he is a servant of Pyron, is also discluded. ANAKARIS, while in theme for the game, is an immortal pharaoh with extreme power over others and reality itself, and is as such not available for application. Q-BEE, being an almost emotionless queen of the soul bees, is bordering on both the absolute edge of allowable theme and playability. As such, she is available only as a plot character.