Hm... if in your fnaf au they work at the pizzaplex, do they interact with the animatronics? Specifically, Sero? How do they get along?
Do they ever find out the truth about what happened to him and the other animatronics/souls, or does it stay a mystery?
Would there be a specific killer in your au like William Afton?
If you're talking about Bakugo, Midoriya, Iida, and Aizawa. Yes all of them interact with the animatronics.
Sero is Iida's favorite, he just finds the lost and found animatronic goofy. Only Aizawa finds out about what happened to some of them.
Keep in mind in this au Sero was the first victim to the killer years and years ago. Unlike cannon Sero's quirk wasn't tape, instead it was something that was able to bring inanimate objects to life called Cursed object. It wasn't permanent but when he was killed it went haywire and basically set a curse on the whole pizzaplex as his spirit was trapped there, binding to the animatronic and the building.
There were a few other victims who inhabited the other animatronics later, only 4, however when eventually the place became a megaplex a few decades later. A few tiles from the old place remained which kept the curse alive alongside Sero's presence. Aizawa made new animatronics and after a while they eventually came to life past their programing.
Aizawa is the only one that finds out about all this and is fully aware that all the animatronics are alive, though only four of them were once human. The other three eventually come to realize that the animatronics are more alive than they once thought but they don't learn the full story.
As for the killer, he got away without being caught, eventually dying years later.