Japanese Language Stack Exchange is a question and answer site for students, teachers, and linguists wanting to discuss the finer points of the Japanese language. It only takes a minute to sign up.
Sign up to join this community
こいつはこっち系のネタにとにかく弱いのだ
The definition I found of 系 (system) doesn't seem to fit here. What does that mean?
As for ネタ, I know it can mean ''joke'' but is it really what it means here? In the official translation, this sentence has been translated as ''She's especially weak to this sort of talk.''
As psosuna notes in the comment, 系 here means something more like "style, type, sort of thing".
ネタ derives as slang from 種【たね】, and originally referred to "seed" as in "raw material from which to make something else". I think ネタ still has this meaning, in addition to the broader sense of just "stuff".
Looking at your sample translation, I see that you may have misparsed とにかく. This isn't とくに ("especially"), but rather its own word とにかく ("anyway").
So putting all that together:
こいつはこっち系のネタにとにかく弱いのだ
She's weak anyway when it comes to this sort of stuff.
