This is the name and short summary about the hakkai chapter. I don't believe it would be the demon that raped kanan because he wouldn't have warn restraints and presented himself as a human and from memory he was a centapeed demon. It could possibly (if it is a man) be Hakkai's and Kanan's father, or maybe someone that knew her before she met Hakkai.

"Honeymoon": A guy talks about a dead person.
Hakkai hears the name of a certain person...