Board Thread:Fourth Databook/@comment-4366149-20141122004623/@comment-25626003-20141203003738

You're right. It's not a chakra nature, but a special kind of Katon manifested through the eyes. It's "Enton", hence "Blaze Release". That's why placing dojutsu next to Enton's icon will ensure that people don't confuse it for a chakra nature.