Futa can be unlocked in galaxy 3, find tentacle monster in Para Ark Warehouse area. In battle, they will perform dick implant to Sasha, select observe to let it happen.
P.S. If you ever set auto skip animation to ON, turn it back OFF
You don't make them use it its entirely rng, so you may see it a bunch of times or only once in a blue moon just hit keep hitting guard until you see it show it up also you only need it once and you need to turn off the auto sex animation for it to work apparently.
it is not in setting, it is an item, a key item in inventory (called Sex Auto Play in Ver0.6x)