Demonic Armament

Soul Sealing Mandate had this to say on the subject:

''It is a term you humans give to those soul armaments with ‘evil’. In other words, they have an evil power you humans see as ‘immoral’, or ‘demonic’, hence their name…But a more unique thing about them is how they can influence the user’s mind. They can make their users more bloodthirsty and even erase the user’s original personality. In the end, the user becomes a ‘demon’. That is the true danger of a ‘demonic armament’.''

''“Through their will, a demonic armament can grow stronger when they kill. And if they kill enough, then it’s possible to gain sentience like a spirit of the armament. In that case, they’ll become as powerful as a Regalia.”''

''“What’s so strange about that? That’s the uniqueness of a ‘demonic armament’. Over two thousand years ago, Tianhun came across a demonic armament that was comparable to ‘Slayer’. Not even ‘Pyro’ would be able to block their attack—Pyro would at least avoid being destroyed.''

''“One has to conquer the evil within themselves before they can use a demonic armament. Otherwise, they’ll end up as a puppet for the demonic armament and become a demon themselves. I strongly advise you to avoid using this soul armament if possible.”''

Potential
Demon armaments aren't restricted to just weapons. Dongfang Ming was able to turn himself into a living Demon Armament and even had a weapon core, his might was comparable to a Regalia in that form.