104th Training Corps arc

104th Trainees Squad Arc is chronologically the second story arc of Shingeki no Kyojin series. After witnessing the horror of Titans, Eren, Mikasa and Armin decide to undergo a military training and enroll into the army as members of the 104th Trainees Squad. There, they get to know the rest of the trainees and slowly begin understanding the hardships of a soldier.

Summary
Keith Shadis, the instructor of the 104th Trainees Squad, psychologically breaking the new recruits as a rite of passage to become effective soldiers. While going down the line, he notices Sasha Blouse eating a stolen potato. As Shadis attempts to understand why she is eating the potato, Sasha splits her potato in half and gives him a piece. Later, Sasha do her punishment of running and would not eat for the day.

Meanwhile, Marco Bott and the other trainees press Eren for details of the Titans. He describes the appearance of the Colossal Titan and Armored Titan. He becomes sick as he remembers his mother being eaten. However, Eren simply attributes this to eagerness to begin his training and kill all the Titans with the Survey Corps. Jean Kirstein interrupts Eren and mocks his decision to join the Survey Corps. Eren does not appreciate Jean's desire to join the Military Police and the two prepare to fight each other.

Sasha who has completed her punishment and falls to the ground. Krista Lenz brings bread for her. As Sasha is practically worshiping Krista, Ymir comes by and Sasha wolfs the bread down before falling asleep from exhaustion. The next day, the trainees begin practicing with the Three Dimensional Maneuver Gear. Eren utterly fails to keep himself steady and takes extra tutoring from Armin and Mikasa. After the dinner, Connie and Jean do not offer any suggestions and Eren goes to Reiner Braun and Bertolt Hoover for help. Although they are reluctant at first, the group exchange their stories of how they first encountered Titans.

The next day, Eren goes back at the practice rigging as Shadis let him try to balance himself on the 3DMG one last time before he will be shipped to the landfills. At first, it appears Eren can maintain his balance and his peers begin cheering, but just as quickly, Eren flips upside down. Shadis has him put back on the ground and after a few moments of contemplation and orders Eren to switch equipment with Tomas Wagner. Eren easily keeps his balance and Shadis reveals his gear was defective, impressing everyone. Shadis mentally notes to Eren's father, Grisha, that his son has become a soldier.

After 2 years, the trainees undergo a fitness assessment. Shadis critiques the overall abilities and teamwork demonstrated by each trainee as they continue the assessment in Titan search and destroy. Then, the trainees practicing hand-to-hand combat as Eren disarms Reiner. As they switch roles, Eren remarks on the useless of learning anti-human combat as well as attacking an armed foe bare-handed. However, Reiner argues that there are situations where soldiers cannot flee and must prepare for any circumstance. He defines this as the responsibility of soldiers and the justification for teaching trainees diverse subjects such as artillery and hand-to-hand combat.

He spots Annie avoiding practice and to show her up, has her try to disarm Eren. When Eren lunges at her, she swiftly kicks his foot out from under him and attempts to leave. But Reiner tells her she must get the wooden knife and over Eren's objections, Annie drops him on his head with a few moves. As she preps to take on Reiner, a grave Eren tells Reiner he cannot back down. However, Reiner is quickly put into the same position as Eren and Annie turns to leave.

Eren praises her technique and her father for teaching her, but Annie believes this training is pointless as it is not a factor in their rankings. She points out the hypocrisy of having the top 10 graduates, the most effective Titan fighters, be the only ones eligible to join the Military Police. As the trainees are eating dinner, Eren is focused on Jean's discussion with Marco on the efficient use of gas in the 3DMG and how such an advanced technique would allow him to be ranked higher and join the Military Police.

Eren insults Jean's shallow reasoning in wanting to join the Military Police and the two almost come to blows. When Mikasa breaks up the fight, Jean is obviously jealous of the attention Eren gets from her and tries to punch him. As Eren gets ready to retaliate, he uses Annie's disarmament technique, quickly ends the fight to resolve the situation. Shadis enters the room to find out what the commotion was all about, Mikasa scapegoats Sasha as letting out a large fart and the situation quietly deescalates.

The graduation of the trainees draws closer until finally the top 10 graduates and those eligible to apply for the Military Police: Mikasa Ackerman, Reiner Braun, Bertolt Hoover, Annie Leonhart, Eren Yeager, Jean Kirstein, Marco Bott, Connie Springer, Sasha Blouse and Krista Lenz. As the graduates are celebrating, Thomas Wagner questions Eren's decision to join the Survey Corps as he sees it as a hopeless struggle with many lives lost. Eren argues that the knowledge about Titans was gained at the expense of those who died and that to throw away their sacrifice would be a disgrace. Eren angrily storms out and is comforted by Armin and Mikasa who reveal they will also join the Survey Corps. When Eren tries to dissuade them, Armin wishes to be useful to the cause of humanity while Mikasa will follow Eren wherever he goes to protect him.

The next day, leaving through Trost District, a crowd of people eagerly await the main force of the Survey Corps to pass, which includes Erwin Smith, Levi, and Hange Zoë. Eren and others watch this and later meet Hannes, who was promoted to Captain, and he congratulates them on graduating before apologizing for his failure to rescue Eren's mother 5 years ago. As the graduates are maintaining the cannons on the Wall, Connie and Thomas reveal their intention to join the Survey Corps after listening to Eren's speech the night before. The graduates are all motivated when suddenly lightning hits the ground outside of Wall Rose and the Colossal Titan appears.