Eren Yeager resided in the Shiganshina District with his parents, Dr. Yeager and his wife. As an only child, he often accompanied his father on medical calls to the Ackerman home, meeting Mikasa Ackerman. During these visits, he prodded Mikasa to explore the surrounding woods, brushing aside her fears by comparing her sheltered existence to her family's chickens. When Mikasa became frightened and cried during one outing, he comforted her as they witnessed wolves devouring three men, an event they later reported to their parents.

Eren maintained a close friendship with Mikasa, who desired more frequent visits. His father began visiting the Ackermans every five days after Mikasa's mother fell ill. Eren frequently arrived with facial injuries from neighborhood brawls, which his father blamed on fights with other children. Frustrated by those content to live ignorantly within the Walls, he passionately described the wonders of the outside world to Mikasa—saltwater oceans, flaming waters, frozen plains, and snowfields of sand. He planned to join the Training Corps with his friend Armin Arlert, aiming to graduate and explore beyond the Walls.

During a visit to Shiganshina, Mikasa delivered a hat to Eren, and they watched the Survey Corps return. Eren attacked two men insulting the Corps, resulting in a brutal beating. Later, he revealed to Mikasa that the Survey Corps had disbanded due to lack of results and the gates were sealed. He ceased his visits because he and Armin were constructing an airplane to escape over the Walls. He gifted Mikasa a caged butterfly, explaining Armin made the cage, and informed her the airplane was finished. He planned to leave that night, promising to return for her once established outside. Before departing, he entrusted Mikasa with his scarf for safekeeping. The escape attempt failed when the airplane crashed into a wall, resulting in his death.