kagerou_project was, initially, the name of a series of semi-connected storytelling songs utilizing VOCALOID software by the producer Jin.
Recently, novels and a manga series have been produced (with talk of an anime adaption), formally naming the characters and elaborating on the story the original songs hinted at. But even though the character tags seem to be in order, there are a couple things that still need cleaning up.
For instance, there are a good amount of pictures featuring kagerou project characters that have the vocaloid song tag (for instance, mekakushi code (vocaloid) but are missing the kagerou project umbrella tag. I was thinking that perhaps there should be an implication in place for these, so that searching kagerou project returns all the relevant images. Alternatively, it could be cleaned up manually.
Besides that, there are many instances of the creator connection tag being used for images featuring groups of the characters from the story together. I'm not sure if this is accurate anymore. All of the characters are from the same universe, and since the debut of the novels/manga, many of them apparently have interacted with most or all of the others in some way in canon. It's not really a crossover for them to be featured together.
Updated by jxh2154