The only artist I'm finding is bosaboy07 from DeviantArt. However, it seems pretty sketchy. His art looks like different styles, so they just may be stolen art. The lack of comments on them also makes me believe it's not his art.
But as Shiro said, it is part of Pixiv Fantasia Fallen Kings. That's as far as I can find.
>>3 Yeah even the Zerochan tag for Pivix Fantasia doesnt have the picture, they usually tag the pivix id or artist name. Maybe they deleted their account?