A big sister is somone who you are extremely jelus of even though you will never admit it she is more popular then you and butiful you mite not always get along but you love her enmyway

a torture device from the depths of hell

A big sister is a little sister that has grown up, and is no longer capable of collecting Adam from corpses. They are in a deep sea diver suit, just like a Big Daddy. They are able to use Plasmids, and have a large needle to take Adam and transfer it into themselves.