[Willliam's not going to judge how Kazuya has his tea too much. It was rather mild compared to Sytry's own habits, which tended to result in the tea being more sugar than actual liquid. He has his own tea without sugar for the moment, taking a few crackers for himself, since he suspects they will be gone rather quickly.

He listens to Kazuya carefully, mentally noting down what he was being told. It wasn't being explained very well, but he could get the gist of it.]

Hmmm, I see. That sounds a little different, but not by much.

[William set his cup aside, having manged to polish off his own crackers rather quickly.]

First off, as far as I have gathered, in my world, Angels and Demons are pretty much the same as well. The only difference is that Demons are those that were cast out of Heaven during Lucifer's rebellion. I do not know the details of why, though from what I understand it is complicated.

[And quite frankly, William didn't care terribly much. Sure, he was a bit curious, but really, what did it have to do with him?]

But because of this, they share a few unique quirks when it comes to their biology. First of all, while they can reproduce as humans do, they have limited amounts of children. So they are forced to increase their numbers though other means. To that end, Demons make contracts with humans, and when those humans die, they become new demons, called Nephilim. Heaven calls their human converts Saints.

[He took some more tea, before going onto the next bit.]

But, most importantly, is the fact that they occasionally have to go to sleep. They live long, immortal lives and in order to sustain this, they enter a time of hibernation, which can last many centuries. If they do not do this on occasion, they will die. It seems they all must do this, no exceptions.

And Lucifer is about to enter his own sleep.

[A long pause then.]

I suppose you can guess how many problems that would cause.