[@Traitor]

1. No, you don't need to learn about Nier Automata to roleplay this. As I said, it's inspired by it but it isn't set in the world.
2. AIs with human emotion were created when Lifeline was created. However, many AIs have different purposes. Hueco was a living library index before he joined Aegis and Dee was for a combat simulation for instance. So if you can find a way to make a robotic AI fit in through their origin, I have no problem with it.
3.The idea you have still sounds like a protector role since it still has the ability to protect allies from attackers. As long as they have some sort of defense oriented skill set, with combat capability, they're a protector.