The Female Titan arc

The Female Titan Arc is the fourth story arc of Attack on Titan series. After the battle, Eren is assigned to the Levi Squad as a member of the Survey Corps. Along with some of his friends, he gets ready for an upcoming expedition. However, beyond the Walls, there is an unpredictable danger awaiting them.

Summary
While Eren is still imprisoned, the news of a Titan siding with humans is spreading. People inside Wall Sina, however, do not want to believe such rumors as they think that an operation to retake the Walls will fail and they will have to cope with refugees and food shortages. Some of them even go as far as to claim that the Titan may side with the refugees. On the other hand, the inhabitants of Wall Rose consider Eren to be their savior and believe that with him, they may even be able to retake Wall Maria.

Elsewhere, Mikasa and Armin learn of Eren's trial. Armin correctly deduces that it will decide whether Eren will live or die, much to Mikasa's shock. Both of them are then summoned to the trial as witnesses.

Zacklay informs Eren that he will be the one leading the trial which will decide his fate. Nile Dok of the Military Police then presents their proposal, which is Eren's immediate execution. As Nile tells Eren to reveal any information he may have, a person next to him, Pastor Nick, exclaims that there is no need for that as Eren should be executed right now.

Afterwards, Erwin states that they want Eren as an official member of the Survey Corps in order to use his power to reclaim Wall Maria. Erwin explains that due to the entrance to Trost District being completely sealed, his plan is to use an eastern route to reach Shiganshina District. Pastor Nick speaks up one more time, angered to see that they want to touch "the gift from God". Armin says that it's due to people like him that it took so long to mount weaponry on the Walls, with Rico Brzenska stating that these people have a lot of power and support.

As people in the room become afraid of the situation to the point when they also question whether Mikasa is human, Eren attempts to defend her and accuses them of making up theories that fit them. Even though he is not sure if it the right thing to speak his mind at the moment, Eren continues and states that they didn't even see a Titan with their own eyes. He then tells them that if they are cowards who don't want to fight, they should at least let him be the one to do it.

At that moment, Nile orders the soldier next to him to point his gun at Eren, but before anything happens, Eren finds himself to be kicked by Levi. Levi then continues brutally beating him up, even knocking out a tooth, all much to Mikasa's infuriation. Levi then states that pain is the best lesson. Nile tries to stop him in fear that Eren may transform into a Titan. Levi, however, replies that he is the only one capable of stopping Eren and asks them whether they would be able to kill him. Erwin then raises his hand and proposes that they take Eren with them on an upcoming mission, with the result of the mission deciding whether Eren is a friend or a foe of humanity. Zackly accepts this and concludes the trial.

At the HQ of Survey Corps, Mike Zacharius discusses the upcoming mission with Erwin. Erwin tells him that they have to quickly prove Eren's usefulness to the central, but Mike sees through this. Praising Mike for his 'smell', Erwin states that he will tell him everything when the time comes.

Later, Hange Zoë arrives to ask Eren to participate in tomorrow's experiment. When Eren asks about her experiments, the squad stands up to leave, knowing what is to come, while Hange is happy to have found someone who will listen to her.

Hange then begins explaining about the two Titans they have captured and the tests being done to them, including attempts to communicate. The Titans were named Sonny and Bean, after a human tribe that used to eat humans. The experiment continued as they tried to deprive the Titans of sunlight. Afterwards, they tested whether the Titans have any other vulnerabilities by directly damaging their bodies, which caused pain for Hange as well. Hearing her talking about the Titans like that, Eren questions how is it that she's able to stay so cheerful around the Titans. Hange explains that she used to hate them as well, but after a certain incident, she realized the mystery of Titans' bodies and tried to look at them from a different point of view since then. Seeing that not only Hange, but whole Survey Corps are people who desire change, Eren asks Hange to tell him more about her experiments, however, even after a whole night, he seemingly learns nothing new.

That is when a soldier arrives to report that both Titans were somehow killed. Everyone rushes to the place just to find evaporating skeletons of two Titans, much to Hange's agony. Apparently, the culprit is a soldier who then used Three Dimensional Maneuver Gear to escape, as Eld and Gunther note. Erwin then approaches Eren and asks him about what he can see there and who is the enemy. This leaves Eren confused, so Erwin apologizes for asking odd questions and leaves.

Later, Erwin Smith stands before the soldiers in order to have them join his branch. He explains about the future mission of the legion and even reveals the information about the basement of Eren's old house, much to Armin's surprise who wonders if Erwin has some hidden motive. However, Erwin also tells him about the grim future of a Survey Corps soldier - in the last 4 years, 60% have died. He ends his speech and then dismisses those who want to join other divisions and as many people begin leaving, Jean, Sasha and Connie state that they already saw how Titans eat people, but in the end, they stay and along with Mikasa, Armin, Reiner, Bertolt, Ymir, Krista and other soldiers salute, as Erwin praises them for overcoming their fears.

The new members then begin their training, however, it consists mostly of remembering Erwin's long-range scouting formation. Eren also learns of this strategy and him and the rest of Levi squad then wonder if Erwin has any other plan that he hasn't revealed to the soldiers. Later, as Eren finishes cleaning, he notices Armin and Mikasa and heads to them to greet them, with Mikasa questioning whether Eren was tortured and the stating that she will take revenge on Levi. Eren then meets up with the rest of his friends and is shocked to see that Jean is among the scouts, but not as much as when he finds out that Marco is dead. Eren then questions if they are joining the operation as well, with Mikasa confirming it. Jean then begins asking Eren about his Titan powers, wanting to know if it's true that he tried to kill Mikasa. Despite Mikasa's reluctance, Eren confirms this and also the fact that he cannot fully control his powers. Seeing how bleak the situation is, Jean states that he wants to know what he is dying for, but in the end, he decides to count on Eren. Some time later, the bell starts ringing as a sign of the gate opening and the beginning of the 57th expedition, as Erwin leads the soldiers outside the wall.