If you want your legs to be unnatural, you need to do unnatural things in the gym. That means you need to have the determination and the mental strength to hit every single repetition. Leave everything else in your life outside the gym. Right now, the only thing you need to focus on is the workout.
These heavy weights and high reps will challenge you beyond what you're accustomed to. Don't quit. Don't go lighter. Don't take the easy route. Your goal for this trainer is to gain mass; you might have to go to a dark place to get there.