The series tells the story of Eren Yeager, Mikasa Ackerman, and their friend Armin Arlert. After the Titans breached the outer wall, including the colossal skinless Titan standing at 60 meters tall and the unusually intelligent Armored Titans, and Eren's mother died as a result of the destruction, Eren swears to avenge the Titans and later volunteers to join the military, along with Mikasa and Armin.
After five years have passed, the graduated trainees stationed in the Trost District, the Titans once again attack one of the border cities adjacent to Wall Rose. In the battle that begins with the defense of the Scouts, Eren saves Armin from being eaten by a Titan, and later Eren himself is eaten by a Titan that appears, initiating a fight against the Titans while the humans ignore the revealed Titan, who turns out to be Eren, possessing the ability to transform into a Titan. Despite being viewed as a threat and assisting the army in reclaiming Trost District, he is put on trial for being a danger to humanity and later joins the Survey Corps in the Special Operations Squad led by Captain Levi. During the 57th Reconnaissance Mission to Shiganshina (the district destroyed five years ago) where the basement containing secrets about the Titans is located, the Scouts are attacked by the Female Titan who tries to kidnap Eren. Although the Scouts capture the Female Titan, she later escapes and kills all members of Levi's squad, forcing the mission to retreat. Armin identifies the Female Titan as Annie Leonhart, one of the military trainees who taught Eren how to fight. They devise a plan to capture her in Stohess District. During this operation, significant damage is caused, and they discover that the Titans are present within the walls surrounding human settlements.
Eren discovers that some of his friends are capable of transforming into Titans and were sent as spies by an unknown party to find what is known as "the Coordinate." It is later confirmed that the Coordinate is the original power to control the Titans, and Eren possesses that power. The royal family and the military police want Eren and his friend Historia Reiss, whose real name is Historia Reiss and is the true ruler of the Walls. The story reaches a stage where a revolution succeeds in overthrowing the monarchy, and Rod's death at the hands of his daughter Historia, who becomes the new queen. It is then revealed that the Reiss family is responsible for creating the walls a hundred years ago using the Coordinate, which was stolen from them by Eren's father, Grisha, who transferred it to Eren by turning him into a Titan before being consumed by his son.
By harnessing the new power obtained through Eren, known as the permanent hardening ability, the Survey Corps manages to reach Shiganshina this time to reclaim Wall Maria and seal the hole. However, Zeke sets a trap for them, leading an army of Titans, including the Colossal and Armored Titans. The battle ends with Zeke retreating, and the Colossal Titan is defeated by Armin, resulting in his body being burned and then injected with a serum while dying, transforming him into the Colossal Titan. However, at the cost of the lives of almost all the members of the Scouts, including the Scout Regiment's commander, Erwin Smith.
Before their return, the survivors of the Survey Corps wanted to visit the basement of Eren and Mikasa's house and found evidence proving that humanity beyond the walls is not extinct as they believed, but rather thriving. However, they also discovered that their race, the Eldians, are oppressed and persecuted by the Marleyans—the ruling race that subjugated them on Paradis Island (the island within the walls) and seized its natural resources. The Eldian prisoners were transformed into Titans to ensure their imprisonment within the walls, and Reiner, Annie, and others among the Titan shifters were sent to steal the power of the Coordinate. Eren also learns that Zeke is his older half-brother, who betrayed their father and headed toward Marley. After the repair of Wall Maria, Eren prepares the others to face Marley's forces.
The story then moves four years ahead, where Marley possesses Titans such as the Armored Titan and the Beast Titan, as well as trained warriors who inherit their powers since the Titan powers have a limited lifespan of 13 years. Marley is at war with another nation called the Mid-East Allied Forces. Despite Marley's victory in the war, it is greatly devastated by a new invention to combat Titans, the artillery capable of inflicting serious damage. Most of the fortress is destroyed by the Titans.