Lynx190 said:
Also I'm developing a suspicion the commissioner and said user are the same person, considering how many of them seem to have been uploaded by him and how persistent he is with the tagging. It really gives me the vibes of artists who slap tags of all the popular franchises on their art to force people to stumble across it (90s search engines and the html meta tag, anyone?) Although I don't notice it on the pixiv source pages in this case, but then pixiv also has a 10-tag limit.
Going through their comment history, I also think the same thing - aside from the fact that they just happen to have the same interests as the commissioner, there's also the fact that they had post #3190135 available to upload for some reason, despite no available source.
In any case the tagger has ended up controlling an artist's tag for some purpose.