Pulse 380 (Patreon)

I don't know if Charlotte is the one everyone expected Connor would pick, but she was the obvious choice story-wise.

She's connected not to a side-character, but to the main character.  Also, when Annie and Tabitha both become C-Class, they'll need to have a third on their team.  Delphi would have been too powerful as a B-Class, but Charlotte is just right.  She also throws the current dynamic out of whack too, as I expect she was sort of in the Tabitha position with Annie and Lucy.