So I love your Fan akuma, Fandoom! Can I ask what exactly is the character's backstory and what inspired her for the fic?
It brings me great joy to hear you say that. Fandoom is my personal favorite akuma that I have made. So, since her back story really doesn't get super fleshed out in the fic.
Vivienne is basically a super fan. She hyper focuses on things that catch her interest. She is ‘That’ kind of fan. The backstory that I didn't delve into is that, Wayham and her were actually co-vice presidents of Adrien’s fan club. Wayham would keep things level when they planed events and it would work out. But after Wayham became friends with Adrien in Gorizilla, he felt weird being in his fan club when he wants to be his friend. So he resigned. Now Vivienne becomes the president and since she isn't checked by Wayham (who surprise was the more reasonable one) she kind of goes overboard and most of the club leaves, save for like 5 people. The thing is Vivienne is really nice, but she loses herself in her passions. People that know her deep down, understand that she isn't a bad person, but she needs a bit of a wake up call.
So when Vivienne (calling herself Adrienne because of her current ‘Phase’) was crushed over the Adrien interview, she was ripe for an akumatization. Which then, thanks to akumatization multiplied her obsession to insane levels.
As for why I created fandoom. I wanted to create a character as an akuma that was meant to represent what an actual obsessed stalker would be. The discomfort Adrien would feel, the inappropriate action taken, the downright self righteous antics. Fandoom was also meant to be a bit of a reference to the most toxic parts of fandoms, what putting a person/character on a pedestal would look like.
That is also the reason why she realizes how far she has taken things near the end, because she was ignorant of how her passions impacted others which is why she started to doubt herself, and when her friend pointed it out, she was starting to understand.