Dude its obvious you don't actually care, and are just trying to get me to say something you can twist around to finger me as a hypocrite.
But okay, here you go.
A while before that Fen had promised Aven that she wouldn't let anything else control her. A promise that if broken Aven might abandon her over like he almost did. Which she would have a serious problem with thanks to a whole other arc before that.
But Problem she didn't want Fio(who was being controlled by Anubis) to go on a rampage. So she offered herself up instead, and did the thing I explained earlier.
Because of it she:
Had to willingly almost break her promise. Which took a bit of courage for her to do.
Got closer to Fio.
Formed a relationship with Anubis.
And got back into touch with the side of her that like to kill things.
PM box is Closed, Indefinitely Friend Code: 3368-4181-6850

[1]
◊