She Noticed AU wasn't its own AU at first.
When I first thought of it, I was writing two MCD fics: one where it was a novelization and the other where Irene was a queen of Angels (and one of them got trapped in Aphmau's body instead of Irene being "asleep").
She Noticed was going to be part of the novelization, and it was going to go into more detail of Zenix, how he became a Shadow Knight and why his betrayal hit everyone hard.
I had Zenix written down as an awkward, but brotherly figure, who slowly deteriorated the more and more everyone saw Aph as the Lord.
The novel version of Aph was supposed to pick up on that, and be concerned, and when he snaps and almost kills Garroth (someone who canonically helped raise him judging by how he stated he found/saved Zenix and that the knight in training couldn't be any older than 19 when Aph came) it must've been like almost becoming a Shadow Knight again.
Or, at least, that's how I headcanon it.
You'll be getting some Zenix flashbacks within the next three She Noticed installments, I promise :)