Who are the Angels already ?

Heya all ^^ I'm a bit lost rn. I'm catching up on the story, and I finished Waifei Peninsula. The next step is the Angels of Delusions... I don't remember them in the story, and yet Phaeton seems to already know a lot about them so... Is it about a limited-time event I missed ?

It kinda feels like I'm doing the Mockingbirds story without ever seeing Victoria Housekeeping y'know ^^"
So what should I do to... get up to date ?