>Twilight Sparkle
I wouldn't be able to do this to her. Twily is my waifu and she has a big heart, this would completely break her.
>Fluttershy
She's so kind and innocent, she never did anything wrong in her whole life, I couldn't do this to her either.
>Pinkie Pie
Same as Fluttershy. She's so happy and innocent, this would completely traumatize her.
So, the only options left are Rarity, Rainbow Dash and Applejack.
>Rarity
She's the weakest one of the three and her magic isn't that strong, so I would simply tie her up and gag her and proceed to rape her tight, virgin pussy.
>Rainbow Dash
She's the strongest of the mane 6 after Applejack, so I would have to drug her with something and tie her to a table with her hind legs spread. Then, when she woke up I would gag her and rape her ass first. She would have the most satisfying reaction, because she would be very angry at not being able to do anything to stop it and sad at having her pride completely destroyed and for this to be happening to her. Then I would finish by cumming inside her.
>Applejack
She's the strongest, so I'd have to drug her too and tie her up with metal restraints and chains. But she would be the most dangerous one, because if she managed to escape, she would surely kill me.