Big Sister

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

The Big Sisters are unusually tall and gangly, since they are at the stage of sprouting from youth to adulthood.[1] Documents from There's Something in the Sea described the Big Sister as 6' 10" (2m 8 cm) tall and having a shoe size of only 7.5. (38 EU and 5 British).

Each Big Sister wears a diving suit reminiscent of those of the Big Daddies, but with their own distinct aesthetic. These suits were designed by Alexander himself, as heard in the Big Sister audio diary. A Big Sister helmet consists of a large sphere with two portholes. Big Sisters are able to withstand immense water pressure and can be seen venturing outside of Rapture as the Big Daddies do, and are able to swim about.

Big Sisters are formidable beings possessing great agility and Plasmid powers. They wield large, wrist-mounted needles on their left arms. These are used primarily for melee attacks and extracting ADAM in a manner similar to a Little Sister's extracting needle, which allows the Big Sister to regain health in combat from Splicers. Big Sisters are the only creatures in Rapture shown to seriously damage the exterior glass windows of the city, something that the weapons used by the player and residents of Rapture cannot do.

The Big Sisters' role is to accommodate, protect, and transport Little Sisters, and they have a cage-like basket on their backs to carry the Little Sisters. The Little Sisters appear to frequently travel with the Big Sisters, and they have taken to decorating their refuges by adorning their cage-baskets with bows and ribbons and drawing childish doodles on the Big Sisters' oxygen tanks.

Big Sisters are mute creatures who only communicate through shrieks, and sometimes light hums if they're comfortable.

Since they're protectors of Little Sisters, they don't usually attack unless they think they're actually a threat.