Mikasa has short black hair and bangs on the left side of her face with dark swirly eyes and is almost never without her red scarf. She wears the typical cadets uniform.
Mikasa is a focused, serious, and reserved individual who does well in her studies. She is determined to prove herself as someone who is protective - especially to the likes of Eren. Her devotion towards Eren is unconditional yet unfathomable, as even he gets confused sometimes.
When Eren is late to class, Armin asks Mikasa if she woke him up, noting the deep bond they share and choosing not to wake Eren so Mikasa could. When he finally arrives, Eren questions Mikasa on why she did not wake him up, with her blushing and answering that she did not want to risk starting rumors by going into the boys' dorm.
Armin faints during the morning assembly and is sent to the nurse's office. Following Eren who went to check on Armin, Mikasa says that she was concerned about Eren not being able to endure the long speech and stay on his feet. He is annoyed by how weak Mikasa considers him to be, and tells her it is nothing when they are being trained to beat the Titans. As he starts heading back, Mikasa is forced to stop Eren by knocking him out.
During the cadets' debut day, Mikasa introduces herself and states that her specialty is carving meat.
In the hallway, the boys are caught with an indecent book. Sasha criticizes them for getting excited over these matters, but Mikasa wonders what type of body Eren likes. Sasha compliments Mikasa and assures her that Eren would like her body type, and she blushes at the thought.
While the girls use the classroom as a changing room, Eren, running late, accidentally walks in on them. Ymir chastises Eren, but Mikasa comes to his defense, believing that he only wanted to see her changing.
Eren is bedridden on the day of the cadets' mealtime pudding. Ymir finds the extra pudding and gives it to Christa, but she refuses, stating that others want it. Ymir agrees to a game of Rock-Paper-Scissors, with Mikasa resolving to win it for Eren. After Armin tells her of a strategy to win the game, Mikasa declares that she is the strongest among them, saying out loud that she will be throwing "Rock," as per Armin's strategy, believing that now everyone will be throwing "Paper" to beat her, and plans to actually throw "Scissors." Ymir is aware of this trick, and throws "Scissors" as well.
In the second round, Ymir wins against Mikasa, but Armin points out that Ymir had thrown "Rock" after she had seen Mikasa throw "Scissors." Mikasa is not giving up and prepares to fight Ymir. However, Christa intervenes and decides to give the pudding to Mikasa after realizing it belongs to Eren.
On the cadets' day off, Mikasa attempts to head into town with Eren and Armin.
Mikasa glares at Annie, who keeps knocking Eren over during their hand-to-hand combat training. Mikasa tells Eren that he should pair and train with her instead, stating that Annie is hurting him more than necessary. He argues that Annie's leg techniques are different from Mikasa's brute strength. Mikasa then suggests for both her and Annie to use their techniques on Eren, and that he gets to decide which one is more effective. Mikasa starts by punching Eren, then Annie kicks him in the face. Eren is left unconscious and both girls prepare to directly face off.
Armin prepares to shave Eren's head with a straight razor, but is stopped by Mikasa, who questions him about it. Eren tells her that he needs to shave his head and act like a real soldier. Mikasa tries convincing him otherwise, then decides to shave her head as well, but he opposes that idea.
Eren gets a low score on his test and is tutored by Armin. After Eren finds all of it easy to understand, Mikasa takes a look at Eren's test result and shows it to Armin, with him revealing that Eren's answers were only off by one row, but still nearly correct.
Marco finds a lost pink bag and decides with the others to return it to the girls' room by sneaking through their room window. As they dangle from the roof, Mikasa briefly senses the boys, but they manage to trick her by mimicking cat sounds. The girls finally leave and the boys enter the room. As Marco places the bag, Mikasa suddenly returns, to the boys' horror upon seeing her.
Eren accidentally spills his drink on himself and Mikasa tells him to remove his clothes so she could wash them, but he questions her on why she always acts like his mother, with her replying that he cannot survive without her, then mentions the times Eren needed her help. Eren exclaims for her to stop smothering him. Stunned, Mikasa leaves while looking dejected. A while later, Mikasa approaches Eren to talk it over, but notices Franz and Hanna practicing resuscitation and wonders if she and Eren should also be doing it.
Mikasa is invited for tea by Hanna and Mina. When the topic of relationships is brought up, Mikasa is asked who she likes, with Mina pointing out that it is obvious, but remarks that he is coldhearted. Mina then tells Mikasa of a special magic spell, explaining that if Mikasa writes a name on the palm of her hand and then keep anyone from seeing it for a full day, she would end up being alone with that person. A while later, Mikasa waves for Eren, but remembers to grip her hand before Eren could see her palm. During lunch break, Eren hands Mikasa a loaf of bread, but she receives it by biting it; she accidentally drops food by trying to eat with her left hand, and later lifts seats with one arm during cleaning.
Eren notes Mikasa's weird behavior all day and confronts her about it. Noticing that she is holding her hands behind her back, he realizes that she is hiding something and tries to get her to reveal it, which results in her punching him reflexly. As she rushes over to him, a Titan suddenly appears and eats them both. Inside its stomach, and alone with Eren, Mikasa is happy that the magic spell worked.
Mikasa attends the 104 Cadet Corps' graduation ceremony. As the senior cadet representative, Mikasa pledges on behalf of her fellow cadets to use the training they have endured for the sake of humankind. Commandant Keith praises Mikasa, telling her that any regiment would be proud to accept her as a recruit. When the Colossal Titan suddenly appears, Eren, Mikasa, and Armin charge the Titan along with a group of other graduates, but they all end up eaten.
- Eren Jaeger - Mikasa deeply cares about Eren and her affection for him often leads her to mistakenly believe he holds her same feelings. While Eren is dependent on Mikasa, he dislikes it when she becomes overly protective of him, and has lashed out at her on one occasion.
- Armin Arlelt - The two are good friends who often enjoy each other's company in classes.
- Jean Kirschtein - Her primary interactions with him relate to his rivalry with Eren. Mikasa is indifferent about Jean, despite his attempts to be in her company.
- Annie Leonhart - Their relationship is implied to be some sort of rivalry. Mikasa confronts Annie during hand-to-hand combat training in order to prove which of the two's techniques are more effective.