Humankind is not the only thing that walks the Earth after the Rapture. As demons and angels started making their homes on Earth and tartarean beasts crawled from that smoking abyss to haunt the dark crevices of the world, humans began to make deals and arrangements to secure their survival in a dark moment, though some truly did find love in unimaginable places.
The most prominent race on Earth is still humans. Though they are outnumbered by the beasts who'd devour or enslave them, they outnumber any one type of other sapient beings. There are two main categories of humans, Cthonics, those who survived the apocalypse in subterranean communities, or the children of same, and the Sheoal, those who scratched out their living on the surface, surviving by hook and crook as their world fell around them. There is no particular mechanical difference between the two, save that Cthonics are generally more familiar with technology, and Sheoal are usually more familiar with the monsters of the Rapture.
The Nephilim are the offspring of humans and Celestials, whether angel or demon. In general, they have no culture of their own, being raised by their parents in whatever setting the raising parent is in. Some nephilim do live in communities of nephilim, but few are raised in these communities. There are many kinds of nephilim, varying by celestial parent, or just basic magical mutation.
Celestials aren't the only extraworldly beings that now move freely upon the Earth, mingling with humans. Djinn, elementals, and mephits, to say nothing of stranger things still, now revel in all the natural phenomena the Earth has to offer, finally unleashed upon it again after centuries. These strange beings are just as likely as celestials to take territory and hold it through intimidation and violence, and lay with humans in exchange for the humans' life, or because the human truly is enthralled by their majesty.