After uploading this, I realized that the post I got this from might not be the actual source- his Twitter feed doesn't have any links to a Pixiv/DA/etc. account, and almost all the other images on his timeline are gachaposting. Image search (TinEye, SauceNAO, Google) returns nothing.

Anyone have any leads I don't?

He posts enough sketches from time to time that I feel it's probably legit.