(1) The Deal

Bobby Singer and his wife, Karen Singer, had only one child together, a girl who they named Helena, Lena for short. Growing up Lena became close to the Winchester brothers and even became like a little sister to them. Because her father didn't want her hunting Lena would sneak out and fight the supernatural with the Winchesters. One day she realized that there was no way to be sure how to kill every supernatural being so she went and struck a deal. In return for a book that told how do kill ever supernatural being she would give something to a demon in ten years.