I believe that "Stalker" tag would be useful. I can think of two example of that would be: Matoi from SZS and Koharu from Koharu no Hibi
Next would be "Mute". A character who is either mute or prefers not to speak. This is different from quiet characters. The characters in question will communicate with other, through means other than speach like emails, writing on paper etc. Examples: Meru from ZSZ, Celty from Durarara!, Megumi from Special A, Rena from Onihime VS
I was also thinking of "Pokerface" tag, but it overlaps with "Stoic" tag. I came up with that idea when I noticed that some of the pokeface characters can't be classified as Stoic (i.e. Ayaka from Witchcraft Works, unless I'm mistaken also the main girl from Choku!).
Also there should be a tag for for tooth sticking out of the mouth. I know there is "Snaggleteeth" tag, but according to the guide it only covers the characters with one fang sticking out. What about all those people who have more of those sticking out (like Touya
who was mentioned earlier)?
P.S. Not all of my character examples are in the database yet.
Edit: Oh wait, did I just necro this thread? I hope this was the right place to post this stuff. If not than sorry.