So . You are in aot world in season 1 when the female titan appeares in the expedition. (you can decide gender name ect you can be eren or anyone you want, make your oc.) but you are a new recruit for sure and you can stop the female titans carnage and save everyone who died in aot like the levi squad for an example. You have the nightmare titan(a titan based one your base titan but you have all the 9 titans abilities including the founding.