Tweet mentions a "Takuji" as the name of the artist but I couldn't figure out which Takuji this is (Danbooru has two listed, and I'm sure there are more out there), hence the artist request.

It seems to be Ootomo Takuji. He tweeted that he drew the characters.

Brightlight said:

It seems to be Ootomo Takuji. He tweeted that he drew the characters.

Thank you! I think at least some of the other artwork I posted are his too.