In this fanfiction, it could be that Bonnie's sickness affects his performance during the night at Freddy Fazbear's. Maybe he starts acting strangely, which scares the security guard even more. And the other animatronics might be confused about what's wrong with him. They could try different things like looking for spare parts to replace the malfunctioning ones in Bonnie that are causing the sickness.
Well, it could be about Foxy suddenly not being able to perform his usual tasks in the horror show. Maybe he has a mechanical malfunction that makes him seem sick, like his joints not working properly or his sensors going haywire.
Chica could also be a main character. She could be the one who tries to comfort Bonnie while he's sick. Maybe she brings him some virtual food or something to cheer him up. And Foxy might be another important character. He could be the one who goes on adventures to find a cure or a way to fix Bonnie. He's the more adventurous type, so it would make sense for him to be the one looking for solutions outside the normal areas in the pizzeria.
Even the kids who visit the pizzeria could be main characters. They might be the first to notice that Foxy is acting strange. One of the kids could be really attached to Foxy and be very worried about him. This kid could try to get the staff's attention to help Foxy or even try to comfort Foxy on their own.
Definitely not a true story. FNAF is a work of fiction that takes place in a fictional world with its own set of rules and scenarios. It's all about creating a thrilling and immersive gaming and storytelling experience, not reflecting reality.