There are no humans in the Demonic realms.

Well, that's not entirely true. Many many many humans come to the Demonic Realms.

They simply can never leave.

They are brought in to feed the trees, and for the Masters, but all are eventually consumed.

There was a time when some Masters kept a few around as a sign of status. The problem is that not only are humans delicious, but also that every demon can sense their emotions, always. It is a constant call to feed, and even those that were kept by the Masters must continuously stop other demons from stealing them.

It was deemed not worth the effort.

Still, a few are allowed to "sneak in" from time to time... much to the enjoyment of all.

-Notes on Humans in the Demonic Realms, by Dzu