Mikasa has dark eyes and medium-length black hair. She wears a light-colored button-up shirt and a long skirt.
Mikasa is a cheerful and an obedient child, tending to be hesitant about going against her parents' word. After quickly becoming close friends with Eren, she feels protective of him and tries to overcome her fears, as seen when Eren gets beaten and she attempts to attack his assailant. Mikasa's strong desire to see Eren again results in her doing a drastic action.
Mikasa lies motionless on the tarp covering a marketplace stand, her vertical maneuvering equipment out of gas. She recalls Armin's words to her just moments ago, where she learned of Eren's death. The cold rain falls on her face, and she thinks back on her life.
In the year 844, Mikasa's mother teaches her a pattern of embroidery passed down throughout the generations in her family. Her mother encourages her to pass the technique down to her children when the time comes. Mikasa curiously asks her father about where babies come from, and he sheepishly claims he does not know but that Dr. Yeager, who would be visiting soon, would perhaps know the answer. When Dr. Yeager greets the Ackerman family and enters with his son, Eren. He introduces Mikasa to Eren, who is nine years old just like her. The adults encourage the two children to play together, and Mikasa regrets that she cannot have fun with her parents. Eren and Mikasa begin to play with toys, and Mikasa tells him that her mother is pregnant and believes she is carrying a boy. Eren says that if the child is a boy, he hopes that he will become a soldier. He reveals to Mikasa that he wants to join the Survey Corps to see the world beyond the Walls. Mikasa asks why Eren would want to venture out where the Titans live, but Eren tells Mikasa to promise him that she will not tell anyone his secret, with her agreeing.
Eren takes Mikasa outside to go exploring. They begin to wander in the forest Mikasa becomes worried, saying that her father does not want her wandering in the forest due to the dangerous animals and the likelihood of her getting lost, but Eren is indifferent. Mikasa tells him that she wants to go back home, and Eren returns to the topic of his dream. Saying that he wants to join the Survey Corps, Mikasa's father hunts, her mother farms and cleans the house, and her brother will become a soldier, he asks her what she plans to do with her life. Mikasa does not know the answer, and Eren is disappointed in her willingness to live ignorant of the world outside of her home.
Mikasa still cannot think of an answer and begins to cry. Eren apologetically hands her a handkerchief, saying that the forest is a safe place and not as big as she would expect. Suddenly, the two hear howling in the distance, and Eren eagerly brings Mikasa with him to investigate. Mikasa becomes afraid, but feels that she has an obligation to witness whatever is happening. The two come across the ruins of a campsite overrun by wild dogs who have killed a trio of travelers and they rush back to inform their parents.
On one of Dr. Yeager's visits, Mikasa learns about Eren's friend, Armin, who Eren says is very intelligent. Eren tells Mikasa that one day he and Armin will see the outside world. The more Eren visits Mikasa, the fonder she becomes of the Yeagers' visits to her home. Mikasa's mother suddenly grows sick and is bedridden for three days. The doctor proposes increasing his visits to every five days, and Mikasa is happy with the turn of events. When Eren arrives, she sees that he has received many injuries to his face. Shortly afterward, Eren explains that the people who fought him were content with living ignorant within the Walls and considered his views heretical. Mikasa wonders why Eren wants to see the outside world, and Eren describes it for her.
Later, a boat takes Mikasa to Shiganshina by river in order to return Dr. Yeager's hat, and upon her arrival she sees Eren in the streets. At that moment, the bell atop Wall Maria rings out, and the two head to the south gate to see the arrival of the Survey Corps, which returns in shambles. Mikasa watches in shock as Eren ends up brutally attacked by two men after he hits one of them for insulting the Survey Corps. That night, Mikasa lies to his parents by telling them that Eren has tripped. Mikasa thinks to herself that she is completely incapable of stopping Eren and decides that all she can do is keep her promise to staying quiet.
While Eren recovers, Dr. Yeager takes Mikasa back to her home. On the boat, he expresses worry for his son and believes Mikasa may be able to change Eren's mind. When winter comes, Dr. Yeager reveals that Mikasa's mother has pregnancy toxemia and must move to Shiganshina so that immediate care can be given. When Dr. Yeager reveals that the two men who attacked Eren were killed in a carriage accident, Mikasa sees images of her parents being attacked in her mind.
Mikasa reunites with Eren after he recovers from his injuries. He tells her that the Survey Corps has been disbanded and the gates to the Walls have been sealed, and that he and Armin plan to fly over the Walls in an airplane left by Armin's parents. Mikasa worries for Eren's safety, but promises to keep his plan a secret. Before he leaves, Eren gives Mikasa his scarf and a caged butterfly. Mikasa asks Eren to survive.
While there is a festival outside celebrating the sealing of the Walls, Mikasa realizes that she cannot remember what Eren looks like, and rushes out the door in hopes of seeing his face one more time. As Mikasa runs through the crowd of people outside she gets shoved and pushed to the ground. Mikasa is grabbed by a masked man calling himself Mirror Man, who urges onlookers to watch him turn Mikasa into a murderer. The man tells her that she must kill him if she wants to see Eren again. Mikasa hesitates but is forced to stab the man with the knife he gave her. The Mirror Man reveals to the festival goers that he was unharmed, but still managed to make Mikasa into a killer.
Later, Mikasa starts to regret not stopping Eren from leaving and walks back to Eren's house and looks in the window to find her parents with her newborn baby brother. Armin arrives out of breath and informs Mikasa that the plane had crashed into the wall, killing Eren. In shock, Mikasa finally awakes from her dream. As she jumps to the ground, two Titans start approaching her from both sides. She starts to think about her memories with Eren, and remembers him urging her to fight. Regaining her will, she readies herself to fight one of Titans, when suddenly the other Titan behind her punches the first Titan.
As Annie Leonhart's Female Titan form falls off Wall Sheena, Annie recalls an interaction with Mikasa during their time in the 104th Training Corps. Mikasa enters the room as Annie is peeling potatoes in the kitchen and asks her about a ring she found on the training grounds, to which Annie confirms that it belongs to her. Mikasa then uses her thumb to reveal a hidden blade in the ring. Annie explains that the blade is for self defense. Mikasa questions why Annie, with her martial arts skills, would need a ring with a blade. Annie explains that there are situations where she cannot rely on just her martial arts skills.
Mikasa then asks Annie of her motive for training, and she explains that like most other people, to join the Military Police and live in a safe place. Annie comments on how Mikasa has clearly joined for different reasons. Mikasa tells Annie that she is different from the others as well, stating that she appears to want to join because she has to. Mikasa she hopes that Annie will never be in a situation where she needs to use the ring, with her agreeing. Back in the present, Mikasa stares back at the defeated Female Titan, then tells Annie to fall.
- Eren Yeager - Mikasa had a strong relationship with Eren since his father had started visiting her family's household to check on her mother's health, and he brought Eren with him every time he visited. As the two had started becoming closer friends, Mikasa wished that Eren would visit her more often.
- Mrs. Ackerman - Mikasa loved her mother dearly. She had taught Mikasa about an embroidery style in their family, as well as how to make dolls.
- Mr. Ackerman - Before meeting Eren, Mikasa often played with her father when he could not hunt during the rainy days.
- Annie Leonhart - The two were in the 104th Training Coprs together. Mikasa was very suspicious of why Annie joined the military. Mikasa violently confronted Annie during her attempt to escape the Walls.