Oh good, Nico was taking this well so far. That put River more at ease with this. It would allow her to explain things to a relatively calm young man who might actually retain the information. This was definitely the preferred scenario as she'd rather not have to help calm him down if he instead started freaking out.
"No, not a god. In this world, there is a war, the Apocalypse as it is according to the Christian Bible. There are things called Seals that are supposed to hold Lucifer in his cage. Some of them have been broken, thus allowing people like you and me to be pulled from our own worlds and brought here. In some cases, it also brings people through who have died, such as in my case. I was actually dead, allbeit for less than a minute, then I showed up here. We don't know why the Seal does that, we just sort of accept it for what it is. And no, we can't go home either. Some have tried, but none have succeeded. There are many others pulled from other worlds as well, it is not just you or me."
River waited, wanting to see how Nico responded to that before she continued on. After all, too much of an information dump at once was generally a bad thing. She didn't want to overload him, so she'd let him digest that and allow him to ask any questions before moving on.