Using "devilish woman" should work better than "succubus".
If I recall correctly, that's how it was in the unofficial novel translations.
It might be that I'm just biased due to the unofficial novel translations though.
As I read too many manga, a girl that have heart in the eye is very dangerous type of girl. A fanatical or brainwashed person. I hope the MC V card remains safe.
I think simply "a seductive girl" will suffice.
Something that works with the "where did you learn that" follow up, but not too complicated for a grade school
So our girl is completely useless physically because all of her Ena is used to feed her Familia? I can see a situation where she gets trapped somewhere where her Familia can not enter and she only survives because of Azure Nova comming in clutch. This will probably be the reason they'll become a team and how the protag will begin interacting more with the other Witches.
Nice scan. Also they don't put manholes in alleyways lol (since there wouldn't be enough room to climb down into given it's between two building foundations).