FNaF AU LORE P1: Backstory & Canon Events
Obsidian was originally designed by both Henry and Afton to "bodyguard" both businessmen from corrupted works (if that were to ever occur in the future >:3)
Henry specifically designed her to be "sentient." In other words, burst with vivid feelings in a way that she could easily relate to humans and replicate human-like emotions with ease. He did this considering the fact that the entire franchise was centered around family-friendly audiences and he didn't particularily want Obsidian to appear dark and disturbing. In a way, he made it so that she could interact with the PG audience (if needed) as to not scare them off, even though she isn't a "well-known" animatronic.
Here's the problem: Afton was the one who came up with the idea of making a bodyguard robot, so he at least wanted some credit. But it seemed like Henry was so caught up in the investors that he didn't remember to give his business partner credit for his support or ideas. And that pissed Afton off. Hence, in an act of revenge, he decided that he would make this animatronic of Henry's "turn" against him, essentially.
When no one was looking, Afton went in and recoded Obsidian so that she would be more interested in guarding HIM rather than Henry.
Basically, if there was an attack by corrupted works, Obsidian would go straight to Afton and protect him, leaving Henry in the dust.
Yet, there must have been some sort of bug or virus when Obsidian was finally activated considering the fact that she came into the world with absolutely no emotion!
The only emotion she felt was seriousness, and she was extremely hyper-fixated on doing her job right.
Obsidian LOVED getting praises from Henry, aka her "boss," despite the fact that she was mainly interested in Afton.
Long story short, Obsi started to decipher the world around her once she became activated. Why was she here? What was her purpose? There were other animatronics there that she had to get used to in order to do her job right.
Once she got all of that down, Obsidian noticed the code to protect Afton, and Afton specifically. When she started to pay special attention to him, that's when she began to fall for him. HARD.
Something important to remember is that Obsidian came into this world emotionless. Understand that the Y4ND3R3 VIRUS can have an incredibly strong possession on its victim, leading to the thesis that there is often rarely a cure. The fact that Afton was able to break that barrier and allow Obsidian to feel affection, sympathy, happiness, etc... is the main reason why she feels so strongly that she must protect him with her life (considering the fact that he is the ONLY living being that can make her feel true emotions.)
Now, what I'm trying to accomplish in this AU is to make William Afton the "good guy." I know that sounds scattywompus, but I've had at least two months to come up with the perfect details that accompany my point.
As sad as it is true, Afton DOES manipulate Obsidian in the very beginning when he realizes that his plan is working. On the flip side, Afton actually looks down on Obsidian for two main reasons:
He belives that Henry stole Obsidian from him. Since Obsi was originally his idea, and his work, he believes that Henry feared that his franchise would overturn to Afton and over one simple idea he would get all of the positive rep, and not Henry. So in an attempt to save his fame, Henry "stole" Obsidian from Afton.
The more Obsidian befriends him, the more she reminds Afton of an old animatronic he used to be best friends with long, long ago. This animatronic was made to essentially make and fix other animatronics alongside Afton, and his name was Vixen. Vixen was one of those friends that acknowledged Afton was psychologically broken, but loved him all the same. He didn't care that his friend was different from everybody else. At some point, though, Vixen randomly disappeared, leaving Afton in a cold-hearted state. After his friend left, he thought there was no one else in this mortal life that could ever want to be his friend and at his side the way Vixen did. Who would want to love a cold-hearted broken murderer anyway?
Obsidian does tell Afton her feelings for him at some point, though. But she isn't one of those "uwu I'm so shy" kinds of people. She's that type that goes, "Listen here you little bastard! I have hardcore feelings for you and it's about time you acknowledge them!"
In my AU, the main reason why it seems like Afton is a villain is because he's so touch-starved. Like, after Vixen left and Obsidian first became a thing he was so cold-hearted just because he lost one of his closest friends. As a result of Obsidian spilling her feelings for him, he is reeaaaaally shocked and perplexed (he didn't think there was anyone else in the world that would WANT to be his friend.)
So he asks her stuff like, "Why me? I'm just a heartless, cold murderer." And she goes on and tells him about how he's the only living person who has made her feel stuff and all that jazz. And shortly after (this is around the time when he's Spring Bonnie) he becomes majorly obsessed with her❤