I hope you don’t mind me publicly posting this, but I’ve seen several people mention it in the tags and it needs to be said.
You are, of course, correct. Furudate’s horror past is, in my opinion, one of the things that makes the manga so unique. It accounts for Hinata’s ‘serious face’ but he seems to also use it a lot when it comes to antagonists. I adore that bit where Oikawa goes from super pretty model to super scary maniac, for instance, because it gives him so much depth.
This makes it that much cooler that the animation keeps to the source material and just goes full horror tropes on this guy, including movements, framing and (I didn’t even notice until @leeva-z-kai pointed it out) sound effects.
Haikyuu is something else, my friends.