Soo, I want some sibling action! I was thinking of maybe this:
My character is a female. She is a twin of your character. Gender does not matter. The twins were really close together ever since they were toddlers knowing every little secret about each other. At about the age of 14, you character goes crazy, doing something horrible (what that is is up to you), and ends up in a mental hospital. At the age of 18, your character breaks out, kidnapping the twin for revenge, hence my character is the one that called the mental hospital, causing your character to be hospitalized.
Eh, just something I thought of now, really wanting to do this. PM me for changes, requests, etc.