Mikasa Ackerman is Eren Jaeger’s adoptive sister and one of the two deuteragonists of the story.
Mikasa is a child who was born in Shiganshina District, she lost her parents at an early age when Titans attacked their hometown, killing all but her and Eren, which were the only survivors at the time.
It is implied that Mikasa knew nothing about them or what they were doing. She learns later on after graduating that they are human eaters (not so far off). She has amazing abilities for someone so young – with superior skills in vertical maneuvering equipment, exceptional strength, and great wisdom beyond her years. She becomes more perceptive to battle situations as time goes on.
Mikasa is a member of the Survey Corps and the leader of the Special Operations Squad within it, a title she has held ever since Captain Levi was demoted after Eren’s “trial”. She is one of Eren’s closest friends and fiercely loyal to him.
In addition to being extremely strong in combat on par with or even stronger than some elite veterans, she also shows great concern and commitment towards all members of her squad and fellow soldiers regardless of rank and affiliation.
Mikasa appears cold and distant towards others when not around Eren. She barely shows emotions other than anger or annoyance, most likely due to having experienced a great deal of loss in her life.