One plot idea could be that the animatronics initially see Mike as a threat but gradually come to understand his good intentions. Maybe Mike has a special ability that allows him to communicate with them in a unique way, leading to a series of adventures where they have to work together to solve a mystery in the pizzeria. For example, they might be trying to figure out the true origin of the strange occurrences in the building.
A different plot might be that Mike is actually a descendant of the original creator of the animatronics. The animatronics sense this connection and believe he can help them regain their true identities or break free from some sort of dark curse that has been placed on them. So they start to protect Mike from other forces that are trying to harm him in the pizzeria.
To develop Mike, you could make him start off as a very skeptical person about the animatronics. But as he spends more time with them, he starts to see them in a different light. You can show his internal struggle between his rational thinking and the strange things he experiences with the animatronics. Regarding the animatronics, each one can have a backstory. Chica might have been programmed with a motherly instinct, and as she gets to know Mike, she tries to 'care' for him in her own animatronic way. This helps to flesh out their characters.
One interesting plot could be the night guard gradually forming an unexpected bond with the animatronics. For example, the night guard discovers that the animatronics have a hidden side that is not as menacing as they seem at first. This could involve the animatronics protecting the night guard from some other unknown threat in the pizzeria.
One interesting fanfiction could be about a female animatronic who has a hidden past and tries to protect the kids in the pizzeria instead of harming them. Maybe she was programmed differently by a kind-hearted technician.
One interesting concept could be the backstories of the human animatronics. For example, how they came to be in the form of animatronics. Maybe they were part of some experiment gone wrong in a spooky pizzeria.
A plot could involve the male reader being the only one who can see the true form of the animatronics, not just their creepy, haunted versions. He tries to convince others that the animatronics are not all bad and that there is a way to save them. Another idea is that the male reader accidentally gets trapped in a virtual reality version of the FNAF world and has to find a way to escape while also dealing with the virtual animatronics. There could also be a plot where the male reader is related to the original creator of the animatronics and has to come to terms with his family's legacy and the dark secrets that come with it while interacting with the animatronics.
One idea could be that Gregory is lost in the spooky FNAF world and Vanessa, who initially seems menacing, actually turns out to be his protector. She could use her knowledge of the place to keep him safe from the animatronics.
One plot idea could be that Female Foxy is initially hostile towards Mike in the fanfic. But as the story progresses, they find themselves in a series of dangerous situations within the FNAF world, like being trapped in a malfunctioning animatronic room. Through working together to survive, they start to understand each other better and develop an unlikely friendship. This could lead to them protecting each other from other menacing animatronics and ultimately changing the dynamic of the entire pizzeria.
The animatronics in FNAF have a complex and creepy backstory. They are believed to be possessed by the spirits of children who met tragic ends at the location where the game takes place.
A more complex plot could be that Tyler is actually a reincarnation of someone who was wronged in the FNAF backstory. The animatronics sense this and are initially hostile, but as Tyler starts to remember his past life, he is able to use his knowledge to try and bring peace to the pizzeria. He might have to face off against an evil force that has been using the animatronics for its own malevolent purposes.
Well, one plot could be that Eleven discovers a new power that only Mike can help her control. It makes them have to spend a lot of time together in secret, away from the others. This creates a really close and intense bond between them as they figure out this new aspect of her abilities.