>>3579386>>3579391>It has nearly almost a null amount of content to work with and there's more stimulating/inspiring pairs in other ongoing media.Before anyone would consider kaworei as something romantic before Shin, if you can consider them both standing there together as such and not think about it as a callback to EoE or a reverse situation with Shinji being the God and them the humans now, there were more people that would think of them as siblings for their AUs.
After Shin, artists, mostly kawoshin artists, made stuff with both as siblings. The bigger example of this is Chika with her 50+ likes tweets and people in the comments going "Yeah! Rei is Kaworu's little sister! I love this interpretation!". And this comes from her crossdresser series that got the interest of regular Eva fans, not only people that like kawoshin.
It just never was that popular as a pairing to begin with
