Big Sister

''“Big Sisters are the new gatekeepers of Rapture: Born from Little Sisters, they don costumes much like their former protectors—the Big Daddy. However, these lithe, broken, mysterious creatures are worlds different from the hulking beasts that inspired their design, and everything from the way their armor appeared to how they cocked their head had to tell the story of their creation.”'' - Deco Devolution: The Art of BioShock 2 - Introduction to the Big Sister chapter.

Eight years after the events of BioShock, the Big Sisters are post-pubescent Little Sisters who have become unstable and confrontational in Rapture's environment. They interact with, manage and protect Little Sisters. Their extreme level of powers go far beyond that of normal Plasmid users, and might be attributed to their growing bodies adapting to the ADAM created in their bodies as children. Thus, they have a much greater natural affinity for the powers that ADAM creates.