I think an important part of tagging systems is that you want some way to store what tags have been considered. Like, this story has "female-protagonist" but no

I think an important part of tagging systems is that you want some way to store what tags have been considered. Like, this story has "female-protagonist" but not "teen-protagonist": someone clearly looked at the characters and applied tags, but does that mean it does not have a teen protagonist? Maybe the tag was created after someone reviewed the story in order to apply "*-protagonist" tags. Maybe that person was only doing "female-protagonist" in bulk. Having a system that can point out unknowns is useful both for search (by including them in results) and for filling in that data (by suggesting those stories for review).