At some point in the story, or maybe mentioned in a spin-off, the main character realizes that she/he have a twin sibling who was separated at birth. Whether or not the main character is interested in learning who their twin is, she/he will eventually find the truth about their separation. The main character might never meet their twin in their lifetime, or by chance meet up and spend the time to know each other.
Any stories that hints the idea that the main character has a twin sibling, will be appreciated. the story should include that twins run in the family in the storyline.
________________ If you've ever thought or said "Nice Guys finish last" and really meant it, then you should probably read this LJ post by DivaLion. It's incredibly insightful whether you're male or female.
From a bumper sticker I like: "If you're gonna ride my ass, at least pull my hair."