Oath

First, all myths, legends, and fairytales you have ever been told are real. Vampires, dragons, fae, sirens, and even creatures without a name all exist. They are decendants of a supernatural creature called shifters. With seemingly limitless power, it would appear impossible to contain such magnificent beasts, however, they have one major weakness. No matter how great their power, they are bound by their word. A shifter's oath is a contract that can never be broken even in death.