jiji_(creature)
Tag for the creature that appears in Jiji (aardvark)'s Twitter profile photo and therefore serves as their avatar of sorts; a blue cube-like ghost creature reminiscent of the ghosts in the Pac-Man (game) franchise. Fan art, especially ones of Kantai Collection, has already turned this avatar into a character separate from the artist.
Whenever this creature appears in fan art or art by other known artists, never use "artist self-insert"; it should be used for its appearances in Jiji's own art per that tag's description. "Borrowed character" can suffice as an additional tag.