The first instance of the filler art was a small panel showing Aun and Chax trying to create a bizarre structure out of ill-fitting blocks (which is sometimes how I feel about the story itself). By the second instance, it seemed clear that I should use the filler to tell a little side story.
I always remove the filler art once I finish a proper entry, so the filler story's progression may only have been clear to those with good memories, or to obsessive archivists. For whatever it may be worth, I have created this page to archive the filler art. Please accept it in the spirit in which it was intended.