Preferably the characters are unaware of their circumstances.
The plot must be serious, so no comedies or anything light-hearted. No typical shoujo demon king/poor human romance or anything like that.
If Yaoi, mark as such.
Examples:
Spoiler (mouse over to view)
Blood+: Main character is a queen of the beings she is made to fight against.
Mahou Shoujo Madoka Magica: The Witches are just "developed" Magical Girls.
Mahou Shoujo Madoka Magica: The Witches are just "developed" Magical Girls.