I get the resistance to dom/sub content, I too dislike it 90% of the time except when done in mild or loving ways. In this particular case, Natalie clearly suffered a traumatic experience that left such an negative impression on her that she is always lashing out at everyone, I'm guessing because its better to hurt people than to allow yourself to be vulnerable and be hurt again.
In this specific case, in order to finally 'tame' Nat, it becomes necessary for the MC to 'take control' literally and figuratively of his relationship with Natalie. In turn, once she allows herself to slowly surrender to him, he is nothing but loving to her. He maintains control of the relationship for now so she doesn't slip back into bad habits, but he is trying to reach her to repair her relationship with her mother and sister while insisting he views her as 'his girl' and will be there for her any time, for any reason and she can depend on him to love and protect her. By the end of her content, she has almost done a 180 with him and while still has a little tsundere in her, she clearly begins to crave his attention and affection, all while he continues to be loving with her.
As for sleep sex, initially it is unavoidable the first time when you are accompanied with Anath, mostly to help power her up, but after that, its 100% optional.