My sister always took care of me, we went to live with our grand-parents when our parents died and since then she always treated me more like her son than like a sister. I take advantage of this, if I make her feel guilty about something she gives me always what I want from her. She can't say no to me, it's something unsolved in her mind. Because of this we have great time together, the first few times I insisted and had sex with her she felt upset but with time it became a very normal thing to us and we love it now.