User blog comment:FairyRaven/Fairy Tail Chapter 353: Exorcism, Review and Commentary/@comment-7405046-20130927131647/@comment-7418318-20130927143547

Hey, I have an idea: Demon Slayers were first created in the big demon civil war by the human-friendly demons to bolster their numbers in their fight against the human-hating demons and a true demon slayer can only be taught by an actual demon... Why does this sound so familiar?

Joking aside, maybe the demon slayers killed the majority of actual Demons and subjugated a few they deemed both useful and of little threat and when someone speak's about "Tartarus' Demons" they are really refering to the Demon Slayers similar to how Sting and Rogue are called "Sabertooth' Twin Dragons".