Doyle, Merry et al belong to Laurel K. Hamilton. Xander, and the entire BtVS belong to Joss.
Demons belong to our nightmares.
This story. . . not sure if I'll want to claim it or not.
"There are worse things out there than the sluagh, Merry. Nightmares that are not under anyone's rule, that walk in the shadows of the world. The humans have never forgotten that the fey exist, but beyond that-- well, consider that in your years in the faerie courts, you had not even heard us mention the demons. . . nor had you heard anything in your years in LA."
"Doyle, its a human you want me to hire."
"He's human, yes. No talent for magic, no sidhe or faerie blood."
"Because it's not always about power. Its about seeing what needs to be done, and then making sure it is done, and that is what Xander Harris is gifted at."
"Fine. Send him in"