Potential source: https://www.deviantart.com/frescholy/art/original-character-914011828 (media asset)
I was originally wary of a Chinese artist using a western site like DeviantArt, but I think it just might be the original source indeed. That account's artstyle is consistent, the quality (resolution, artifacts) seems reasonable for a first-party upload; moreover that version is less watermarked than this one.

Speaking of watermarks - I can see a BCY watermark in the bottom right corner. Baidu's reverse image search engine gave me some potential BCY sources. That being said, with BCY being already closed, I can't verify if they were original or not.

EDIT: I looked into the DeviantArt file's metadata, and now I'm pretty sure it's an original source indeed. There's clearly text layer names there, along with folder names. Stuff like that would make little sense to have in a 3rd party source. It's also wayyy larger than this one.