C1463 Hidden Branch

We're at the end, and it's good that we talk to each other in low voices, and no one in front of us can hear us. I first asked the old man about the origin of this Fire Devil, because up until now, I haven't even bothered to understand it.

The old man said that this thing isn't actually a real demon, but what is the standard of a demon? Up until now, there hasn't been a unified definition