Mikasa Ackerman (ミカサ・アッカーマン Mikasa Akkāman) is the adoptive sister of Eren Yeager and one of the two deuteragonists of the series, along with Armin Arlert.
Mikasa appears for the first time in year 845 somewhere inside Wall Maria. She is seen waking Eren up, telling him that they need to return to home. She is surprised to see tears in his eyes and asks why he was crying. On their way home, they meet Hannes. Mikasa watches as Eren complains about the soldiers slacking off while on duty. Later, both Eren and Mikasa watch the return of the Survey Corps forces, witnessing yet another failure of their expedition. After returning home, Mikasa tells on Eren, revealing to his parents his desire to join the Survey Corps. Annoyed, Eren leaves, with Mikasa following him. They save Armin, who is being beaten by local bullies and together discuss their desire to go outside the Walls.
At that moment, the three kids witness the sudden appearance of an extremely tall Titan peering over the top of Wall Maria. The three are stunned to see one that large, only coming back to their senses when the Titan breaches the Wall’s gate. Mikasa and Eren run back to their home to find it crushed and their mother trapped under the debris. In spite of their attempts, Mikasa and Eren are unable to free her, Hannes rescuing them as a Titan devours their mother. Mikasa and Eren are placed on a ship just as the Armored Titan breaks through the inner gate, letting the Titans inside Wall Maria. She witnesses Eren’s vow to kill all the Titans as they are transported to safety.
After the events of the Wall Maria’s destruction, the government’s desperate attempt to reclaim the lands using the refugees leads to nothing but more casualties. This prompts Mikasa, Eren, and Armin enroll with the army and become members of the 104th Training Corps.
During their training, Mikasa helps Eren as much as she can as he initially fails to grasp the basics of the vertical maneuvering equipment. They manage to pass the qualifying tests, Mikasa quickly proving her skills and is praised as one of the best trainees in military history. At one point, Mikasa asks Annie Leonhart, a fellow trainee with exceptional skill, to teach her a self-defense technique that she was teaching Eren, which eventually calls for a bet with the 104th Training Corps to see who is the stronger fighter. At the 104th Training Corps’ graduation, she is ranked first in the class.