It's frowned upon to have romantic interest in your relatives.
Susie sees her brother Tom undressing one day at home and crushes on him.
Susie wants to be around her brother Tom more.
Susie tells Tom how handsome he is and how much she likes spending time with him as a friend.
Susie touches Tom in a romantic way and admits her desire for him.
Susie and Tom hang out more and develop their sibling bond while dating other people.
Susie and Tom have very sick children who need medical care for life.