Big Sisters are tertiary antagonists in Bioshock 2 and its online prologue, There's Something In The Sea. Like their predecessors among the Big Daddies, the Big Sisters were created to safeguard the Little Sisters from harm; however, the Sisters are much more active and far more aggressive than their lumbering counterparts - and much more dangerous. For this reason, they are employed as elite security for the Rapture Family and specifically deployed against Subject Delta as he progresses through the game.