Mikasa wears a yellow school blazer. She has a small blue bow on her school uniform and a short black skirt. She has her red scarf with her on a daily basis.
She is Eren's childhood friend and is very protective of him, wanting Eren to have a normal school life. Mikasa is so attached to Eren to the point where she becomes very depressed if he is not around. Her depression is so strong that it also affects those around her as well. Mikasa is a very mellow individual who is sometimes thought of highly by others. She is a dependable person who is very capable of getting things done.
Mikasa wakes Eren up for his first day of school and finds him drooling. She runs out the house first and calls for him to hurry. While on their way, Eren orders Mikasa not to tell anyone about him drooling. She ignores him and says that she will not tell anyone about him putting his pants on backwards. Eren crashes into several people along the way and Mikasa devises a crashing plan so she can dreamily help Eren up. She runs at top speed to find another route but accidentally collides into him too hard, sending Eren flying. She runs after him and they reunite at the school. She and her classmates run to the Titan side of Titan Junior High School, where they find a giant classroom and find life-size stationery dropping from desks. Mikasa evades them and is later found by Hannes, who directs them to their class at the human side of Titan Junior High. Mikasa attends the opening ceremony.
During springtime, Mikasa and Eren plan to go see their friend Armin. Like the rest of her classmates, Mikasa is warned by Mr. Keith to turn in her club admission form in the next day. Afterward, Mikasa and Eren buy Armin food but are confronted by a Titan, who steals their food. They are rescued by Levi and retrieve their food, with Mikasa catching Eren in her arms after his fall. When Mikasa and Eren let themselves in, Mikasa convinces Armin to come out of his room by mentioning food. Mikasa sweats furiously with her scarf on due to the number of heaters in Armin's room. When Levi opens the window to snatch Armin's futon away, Mikasa cools down quickly in relief. She and Eren head downstairs to find Levi, but Mikasa only finds a button which Levi accidentally dropped. Eren leads her and Armin to school where they find the Attack Junior High Scout Regiment. When Levi is summoned, Mikasa eyes Levi angrily as he smacks Eren in the head with a paper fan. Mikasa joins the Attack Junior High Scout Regiment due to her devotion to Eren. The next day she finds that she is assigned a club membership in the Wall Cleanup Club due to the Junior High Scout Regiment's unauthorization.
Mikasa participates in her school dodgeball game but notices that Eren is absent. She eventually becomes unable to play due to her sudden depression and sits out the game, narrowing down her team's chances of winning. She borrows Armin's futon as a blanket and lies in the corner sulking. Eren arrives late and Mikasa becomes revitalized, ready to help her team play against Annie's. She saves Eren repeatedly each time Annie aims for his face, proving that the two are in a stalemate. Later, Mikasa has lunch with Armin and Eren. Annie joins them and offers Eren her cheeseburger steak. Aggravated, Mikasa forces vegetables and fruits down Eren's throat to prevent Annie from offering any more food.
Mikasa is forced to clean the windows along with Eren and the rest under Rico's supervision due to the Scout Regiment's illegal authorization. Later upon witnessing the Wall Cleanup Club's secret weapon, she goes to finish her task with the group. Following the trust they gained from Rico, Mikasa alongside the group undergoes the training of the omni-directional mobility gear.
She observes and at the same time warns Eren about his repetitive downfall. Mikasa unravels the truth on Eren that he has to give up on his goal by stating that he may have the determination but lacks the abilities to do so. Out of the blue, Armin points out that Eren's broken gear might be the cause, alongside with Rico's denial. After raving about the history of the gear, Rico notices a busted spring in Eren's gear. Mikasa threateningly asks Rico about the real deal behind Eren's gear, terrifying the president. Subsequently, Hannes' crash, Rico declares the broken gear and dismisses the activity.
The following day, Mikasa notes Eren's happiness is because he can clean the Wall with her company. Further on as Sasha senses a tremble, Mikasa along with the others hide behind trees. Upon learning the real purpose of the club, Eren grabs the broom from Mikasa as she tries to stop him. Ill-fated, Eren falls face down in red paint as Mikasa approaches to comfort him.
When Sasha flunks all of her tests, she tries asking Mikasa for help in studying, before Mikasa quickly follows Eren to the Scouts club.
Eren remarks that Mikasa's hair is growing too long, and Mikasa complies with his suggestion to cut it, but Jean stops their conversation by grabbing Eren's shirt and makes a nasty retort. Mikasa stops their bickering by picking Eren up and walking away in silence. Mikasa and Annie later come into conflict and make cold remarks about each other when the latter tries talking to Jean.
Mikasa and her classmates compete against their upperclassmen in the school's Sports Day. When her classmates lose hope of winning against the upperclassmen, Mikasa goes on about how she is strong enough to annihilate them, and chastises the rest of the team. Participating in the last game, shoulder wars, Mikasa swiftly takes multiple opponents' bandanas. With her wearing a raincoat, Mikasa's team then runs next to Petra's, and, under her raincoat, Mikasa reveals a set of stuff that irks Petra, distracting her long enough for Eren to take her bandana.
The upperclassmen plan a sudden "Test of Courage" event, and Mikasa goes with Eren's group to the art room. Hearing a disembodied laugh coming from a painting, the boys run out of the classroom, terrified, while Mikasa remains unphased. In the music room, she translates what Armin murmurs about a ghost that plays the piano. She later follows Eren after he runs off on his own, arriving at a staircase. Mikasa translates what Armin murmurs about a cursed mirror after Eren starts screaming about it. At the gym, everyone starts running around as ghosts and a giant cannon appear chasing after them. It is later revealed that the event is a prank played by the upperclassmen.
Mikasa visits the summer festival with her classmates. Arriving at a shooting game stall, Mikasa easily wins at the game from her first try, and chooses to gift Eren her prize; Big Pork Fillet Cutlet. A sense of rivalry sparks between her and Annie and they both compete against each other, winning every prize in the stall. Mikasa later participates in die-cutting with her friends, and watches as more festival fireworks are set into the sky.
When Eren and Jean fight about who will become the new student council president, Mikasa breaks up the fight by picking up Eren and taking him outside. She later watches as Armin creates a design for Eren's election poster. A few tweaks by Eren result in a disfigured-like design, to Mikasa and Armin's shock. Eren excitedly asks Mikasa of her opinion, and Armin thinks to himself that Mikasa should tell him what she really thinks, but she replies that it looks good, to Armin's horror.
Later, the election candidates run after a student for her notebook and Mikasa joins the pursuit, and catching up to Reiner, she pulls his arm, flinging the notebook off his hand, making way for Eren to jump for it.
Mikasa helps Eren by working in their class' cheeseburgers stand for the school's 104th festival gourmet competition. When their stand becomes popular, they are overwhelmed by tens of orders. Eren says even Mikasa cannot handle that many, and looking at Rico's stand serving customers faster, Eren laments the situation, before Mikasa says she can do it, and starts rapidly flipping multiple burgers at the same time.
When a horde of Titans invade the area and steal all of the food stands, Mikasa rushes to Eren's side, as he cries for his stolen chee-burgs.
Mikasa accompanies Eren to the Titans' building to retrieve their chee-burgs. They head to the principal's office after Hannes points them to it. In there, they see a giant key inside a walled town and a door with a matching keyhole further ahead. Mikasa distracts a Titan while Eren pulls the key. She later watches as Eren inserts the key and successfully opens the door.
When the Colossal Titan lifts the roof, taking their chee-burgs stand and opening its mouth to eat it, Eren jumps at it and is swallowed as well. Mikasa falls to her knees in despair, before the Titan spits Eren out, and he happily announces that he managed to retrieve a chee-burg. Mikasa later celebrates their victory with Eren and the others.
- Eren Jaeger - Mikasa takes the role of Eren's friend very seriously, as she often tries her best defending or protecting him even when he does not need it. Although, those feelings are the only ones she can comfortably show; in reality, Mikasa's feelings for him are more serious. She craves Eren's attention and presence, otherwise she will be in a dire state of depression.
- Armin Arlelt - Mikasa and Armin were close friends ever since they were young. Mikasa respects Armin and, like Eren, wants to motivate Armin to recognize his full potential. To show that, she is supportive of his choices.
- Annie Leonhart - Mikasa is oftentimes jealous of the attention Annie is giving to Eren. She is first uneasy of Annie's actions, but their relationship soon turns into rivalry.
- Levi - Mikasa has a defined hatred for Levi. She shows this with her morbid reactions when Levi smacks Eren when he threw the plastic bottle in the paper waste bin, death-glaring Levi.
- Jean Kirschtein - Mikasa considers Jean as her classmate and is often the peacemaker whenever he and Eren argue. She seems to not notice his feelings for her, however shuts him down unknowingly whenever he tries to make a move.