I have a strong, strong feeling that the magic being REDACTED here is actually Microkinesis! It's a term I've heard mentioned a few times in the past in relation to Dragonsteel and Yolen, a magic that allows the user to see microscopic things and interact with atoms/molecules at will. In the fifth chapter, Jerick looks at small crawling REDACTEDs on a corpse, and recognises them from a man dying of a disease. I thought these were deathspren or rotspren at first, but then I realised they could be microbes. Later on, he uses something vision-related to determine that a Sho Del's armour is steel as opposed to Dragonsteel, which I think he's doing by actually looking at the molecules in the armour.
If I'm right, it seems likely that the initial flurry of REDACTED when Jerick does something to an arrow is him transmuting the arrow into another substance, which i'd expect Microkinesis to be capable of. Probably it's mechanically similar to Soulcasting and slatrification. Considering chapter 6, it could also be something nuclear in nature, which I believe WoB has said is possible with Microkinesis. Any thoughts? I could be way off the mark here, but I feel it's likely.