Mikasa Ackerman originates from the main *Attack on Titan* narrative, with her early childhood explored in the spin-off OVA *Attack on Titan: Lost Girls*. Before the main series, she lived cheerfully and obediently with her parents near Shiganshina District. Her mother, pregnant with Mikasa's brother, taught her family embroidery techniques for future generations. Her hunter father played with her on rainy days. Dr. Yeager's visits introduced Mikasa to Eren Yeager. The children bonded closely, with Eren sharing his dream of joining the Survey Corps. Despite parental warnings, Eren persuaded Mikasa to explore the nearby forest, where they found a campsite attacked by wild dogs. Mikasa developed a protective instinct towards Eren, especially after witnessing his assault by men insulting the Survey Corps. She lied to his parents about his injuries, feeling unable to curb his recklessness but committed to keeping his secrets. After recovering, Eren revealed plans to fly over the Walls with Armin Arlert using an airplane. He gave Mikasa his scarf and a caged butterfly, asking her to promise he would survive. During a festival celebrating the sealed Walls, Mikasa panicked upon forgetting Eren's face and rushed into the crowd. Confronted by the Mirror Man, she was forced to stab him under threat of seeing Eren again. The Mirror Man revealed the act unharmful but declared her a murderer, compounding her fears for Eren. Armin then informed her of Eren's death in a plane crash, leading to despair before she awoke from this memory sequence.

During their time in the 104th Training Corps, Mikasa questioned Annie Leonhart about a hidden-blade ring found on the training grounds, probing her motives. Annie stated her goal was joining the Military Police for safety, contrasting Mikasa's reasons tied to protecting Eren. Mikasa noted Annie seemed driven by obligation and expressed hope she would never use the ring. Annie later recalled this encounter while falling from Wall Sheena.

Beyond the OVA, Mikasa's character arc was defined by her parents' murder by human traffickers when she was nine. Eren Yeager rescued her, urging her to fight for survival and awakening her latent Ackerman abilities, granting exceptional combat instincts and physical prowess. He gave her a scarf, a lifelong symbol of comfort. After rescue, she lived with the Yeager family until the fall of Wall Maria killed her adoptive mother, Carla. These losses solidified her view of the world as cruel yet containing fleeting beauty, embodied by relationships. Her devotion to Eren motivated enlisting in the military and joining the Survey Corps. Mikasa graduated top of the 104th Training Corps, renowned as a prodigious soldier valued for strategic mind and combat efficiency. Her abilities were highlighted confronting the Female Titan to protect Eren and battling the Armored and Colossal Titans reclaiming Shiganshina. Over time, her character evolved beyond sole focus on Eren. She formed friendships like with Sasha Braus and demonstrated leadership. When Eren initiated the genocidal Rumbling, Mikasa joined the alliance to stop him, killing Yeagerist soldiers like Floch Forster and culminating in confronting Eren. In the Paths dimension, she experienced an alternate reality of peace with Eren but rejected this illusion. She assassinated Eren, kissing him farewell before his death, freeing Ymir Fritz and ending the Titan curse. Mikasa buried Eren under a tree near Shiganshina. She visited his grave regularly throughout her life, wearing the scarf he gave her, and passed away peacefully of old age, still honoring their bond.