So, this tag exists: tabris (evangelion). I found it under the Nagisa Kaworu wiki.
Its wiki confuses me, to say the very least. Upon searching for pictures of Tabris' "true form," only images of Kaworu come up - in both English and Japanese. No where does it say that Tabris is a female.
Upon further research, I find that this tag exists: Tabris-XX. It seems more fitting to what the tabris (evangelion) wiki was saying and has more posts than the former tag. Most people tag both of these tags in posts under tabris (evangelion), although there are some posts under tabris_(evangelion) alone that show the "Tabris" name simply being used for Kaworu when the other Angels are present in the image.
Can someone more familiar with the series clarify? I have a feeling the tabris (evangelion) tag should probably be aliased to just Nagisa Kaworu after being cleaned up, but again, I don't know for certain if maybe there is a "true form" Kaworu/Tabris has that maybe looks a lot like Tabris-XX? Or did whoever make the wikis for these tags just misunderstand?