It looks like a bgm visualizer but I think it only appears that way -- the effect will be very active during mellow tracks or at the beginning of a track where very little is actually going on, and sometimes appears mellow at the apex of the song. All this makes me wonder if it's actually a visualizer or if it just seems to be.
Featherman or not the black mask does resemble the berserker armor helmet a lot, too many design choices that fit... The teeth, the hound like ears, the red visors and not to mention Akechi goes psychotic when he uses his black heist suit. Yes, it is like a black featherman but the mask is way too identical to the berserker armor helmet.