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Mitras (ミットラス王都 Mittorasu-Ōto?) is the area of land surrounded by Wall Sheena, the innermost of the three Walls, and the capital of the nation of the Walls. It is the residence of the King and upper-class citizenry.
After the failure of the 57th expedition, Eren Yeager is supposed be returned to the Inner District for judgment. However, he never arrives. The true purpose of the trip is to expose the true identity of the Female Titan, Annie Leonhart and she is revealed in Stohess. After being discovered, Annie attempts to scale the Wall, but she is stopped by Eren in his Titan form with the aid of Mikasa Ackerman. Part of the Wall suffers damage and reveals a Titan within it, but is quickly covered up at Nick's urging.
Erwin Smith visits the capital in response to a summons by the chancellery. As he rides in a carriage with Nile Dok, he is surprised to see that child thieves are common now, even in Mitras. His meeting goes poorly as he discovers the government officials are more interested in protecting their authority than the rest of humanity. After Erwin is arrested for the alleged murders committed by the Survey Corps, he is brought to Mitras for his audience with the king. Public gallows are erected in expectation of his execution. Nile tells Erwin that he expects Erwin to be dealt with at the same time the Survey Corps is disbanded.
Erwin defends the necessity of the Survey Corps to the king and the other high ranking members of the Royal Government, but his words fall on deaf ears. Seeing that they are unmoved, he asks if they have a secret plan as an alternative. The officials redirect the subject to the deaths of several members of the Military Police Brigade at the hands of Levi and advocate his actions as a threat to the peace. There is no need to tolerate such a group within the Walls. They then give the order for Erwin to be taken to the gallows.
Before that can happen, Anka Rheinberger bursts in announcing the fall of Wall Rose and that refugees are fleeing towards Wall Sheena. Dot Pixis immediately calls for his soldiers to secure an evacuation route, making it a top priority. However one of the officials countermands his order and commands that Wall Sheena be shut to all refugees. Nile protests that doing so will sacrifice half of humanity, but the officials do not care because that number of refugees might be enough to spark a civil war.
The Military Police begin to reluctantly follow orders, when Nile declares that he will stand with Wall Rose, even if it means opposing the crown. Commander-in-Chief Darius Zackly enters the room with an armed entourage of soldiers, announcing that he will join him. Zackly explains that the previous report was inaccurate and no Titan attacks have been confirmed.
When the officials protest, Pixis admits to orchestrating this charade as a test. Had they been worthy, he and the other soldiers would have confessed to treason, but since they failed, the military will be a fitter ruler than a group of men who do not value humanity.
The Berg Newspapers' Extra Edition finishes dismantling the government's credibility with its report on the Interior Military Police; how they threatened the Reeves Company and framed the Survey Corps for murder. It blames the royal government for pressuring all other news outlets and accuses King Fritz of being a pretender to the throne.
Erwin is freed and the government officials apprehended. The military announces their seizure of the capital from atop the scaffolding where Erwin was to be executed. Nile tells reporters that their goal is not to establish military rule so much as to restore the true royal family to the throne and regain the people's trust. He lets them know that they are now free to ask questions as the men who used to suppress them are now in jail. However the population is nervous because they do not know what to believe in or whether the military will eventually relinquish power.
Zackly and Erwin leave the crowd to Nile and depart in a carriage. Erwin expresses regret over the coup d'état because no matter how corrupt the government had been, it had kept humanity alive up until the present day. Zackly is surprisingly insightful about Erwin's true motivation. Like him, Erwin values his own life over the fate of humanity, and that is why he was willing to let others choose the harder path instead of giving up and leaving everyone on the easy one. Erwin remembers his childhood dream regarding the truth about humanity's escape to the Walls.
After the defeat of Rod Reiss, and Historia Reiss declaring herself the true ruler of the Walls, her coronation is held in the capital in front of a large crowd. She is admired for being the one to stop her father and defeat a Titan twice the size of the Walls. The heads of the military kneel before her and she stands proudly to a thunderous cheer.