It is rumored that Demonic Artifacts and weaponry all contain traces of true intelligence. They are rare enough and precious enough that very few are willing to experiment on them in case they are damaged.
There was however an incident in which a very wealthy city state gathered up a hoard of demonic weapons and with the help of some of the greatest artificers they could find proceeded to combine them into a monstrous "armor" that could be controlled by a pilot.
The ruler of the city state entered into the "Demon Armor" and activated it. The city was destroyed by its own ruler, who proceeded to then carve a path of devastation before vanishing into the center of the continent.
Some believe that the ruler went mad, but others believe that the armor itself came alive, and simply acted out on its only desire.
-Adventurers Guide to the Continent, on "Advanced Weaponry"