Fun fact: Hifumi was originally intended to become a part of the Phantom Thieves, but with the release deadline approaching and the game's development dragging on, the developers decided that adding her story arc would make the game far too long, so they reworked her into being a confidant instead.

I admit, I'm not sure how common this knowledge is, but I saw the picture and though I would share some trivia.

That really does explain why literally EVERYONE starts talking about her out of the blue, which is basically what happens with every new recruit.