But ... whatever it is, it at least has to be a noun. It can't be an adjective modifying something else, because it itself already has the "of Chaos" attached to it.

I almost want to say it's a compound word trick--Aves ... Kellar? Bird-killer? It wouldn't be past Anghel to freak out and call a random food vendor that. However, A) "kellar" still isn't a word in any language of which I know, B) going off some weird sounds-like thing like that would be a stretch even by "Operation Hatoful" standards, and C) if you already have a bird-killer, one would think that having a chaotic one would be somewhat redundant.