Isn't "aitsu" referring to one person? (presumably Kongou)
If it was for "them" she would have said "aitsura", correct?

wererat42 said:

Isn't "aitsu" referring to one person? (presumably Kongou)
If it was for "them" she would have said "aitsura", correct?

They can be a singular and plural in English, especially as a gender-neutral pronoun.

While it's generally used with a group identifier before it - e.g. "When I wave at someone, they wave back"; I.e. here, it could be said that (Out of the shipgirls,) they've been...

It's a bit clunky, yes. But since Nagatsuki used a non-specific singular, it's kinda limited in English. You could substitute with 'guy' (in the casual, non-male sense) or 'girl' if we were sure, but in the general case, 'they' can be used.

Making it 'they' also abstracts it out quite nicely compared to a gendered pronoun. Which あいつ does as well - using 'she' would imply too much familiarity and certainty with the statement, which is not implied with the use of あいつ.

あいつら is indeed an informal non-gendered plural pronoun, though.