Christian Grey plays a counter dependent Covert Narcissist with unusual sexual tastes. Grey is the colour of the Borderlines and shades of grey is an old Borderline expression referring to the spectrum of Borderline type narcissism.
When I watched the first movie I strongly related to his desire for Ana. Personally I get it exactly. I felt a very personal connection with hat story because it reflects my own story and the women I chose.
I think he chose Ana for the same reasons I chose my GF. She is not powerful, she is innocent, she is extremely submissive, she can be twisted and turned in any direction. She will idolize you but at the same time Grey falls into the same trap of underestimating her much the same way I did. You can only push people so far before they fight back.
Grey could have almost any woman. He could have a model with money but he chose a woman that has 0% sexual experience, not very pretty but kinda cute and has pretty much no money and no backbone. He wants to completely dominate her. He wants to mold her like clay into exactly what he wants. He thinks he can and has the right to because he is so much more powerful than she.
I related to Grey much more as a narcissist than a borderline because it resonates so deeply with myself. Ana is not a codependent though. I thought maybe she was the borderline. Its hard to tell. She secretly has a backbone that makes her feisty and the way she fights back makes my mouth water

Everything about that story is hot and passionate and she is the perfect submissive partner but not TOO submissive to the point of allowing herself to be abused.