Yes, I know human males don't go into heat.
But Vulcans do. It's called "Ponfar." It happens once every seven years of their adult life. And as I happened to have had a great deal of exposure to Star Trek in my formative years... naturally the concept found a way into my writing.
Demons aren't human... and they aren't Vulcan. They're something else... and their biology would reflect that. I called it "heat" because... the blood has a tendency to "boil" and the whole effect denotes passion, which, as we all know, is hot and sweaty... and as the whole thing is based on PonFar, it isn't completely like it. So I needed a word that would describe it. A better term for it would be "atsui" which is Japanese for "hot" which would be closer to the term a Japanese speaking demon would use for his condition.
I am currently re-writing the series to incorporate the word "Atsui." (Along with other revisions.)
--Lel