|Humans will continue to fight one another until the day there is one human or less.|
|— Erwin Smith comments on a song about when humans will stop fighting|
Eren Jaeger learns the history of how he obtained his Titan and how five years ago his father, Grisha Jaeger, slaughtered most of the Reiss family in order to obtain their power, which was held by Frieda Reiss, the elder half-sister of Historia Reiss.
Meanwhile, the military learns that certain bloodlines are immune to the "Scream" that can alter humanity's memories and that if they do not rescue Eren they may soon forget their coup d'état ever happened. Squad Levi arrives at the rural chapel above the underground one where Eren is being held. They prepare to attack while the Anti-Personnel Control Squad waits for them below.
In the Underground Chapel, Eren Jaeger struggles to free himself as Historia Reiss approaches. She tries to reassure Eren and says that her father is an ally to humanity, and that they were wrong about him. Historia says that her father had no choice when it came to the orders he gave regarding the Scouts and the killing of Pastor Nick.
Rod Reiss arrives and says that he will explain the rest, causing Eren to remember his kidnapping and wonder how much time has passed. He notices the unusual glowing crystals that form the walls of the cavern and realizes that this place seems familiar to him. Rod picks up on that and explains that though this is Eren's first time here it would not be strange for him to recognize it.
Rod and Historia place their hands on Eren's bare back, causing him to experience memories of being here before. He sees Rod and his family in the underground cavern, a Titan, a burning chapel, a Scout, his father's key, and himself as a child, turning into a Titan, and eating his father. Rod asks Eren if he now remembers his father's sin.
Years ago, Historia would be visited at the farm by a girl with long black hair, who helped her learn to read. She encouraged Historia to be more ladylike, like a girl in one of her books named Christa. Christa is kind and always thinks about other people. Because the world was in pain, the girl with black hair suggested that Historia become someone who was helpful and loved by everyone. Historia then asked if she could be like her, to the delight of her companion. The girl then apologized because she had to leave and wipe Historia's memory until they could meet again.
In the present, Historia reels as her lost memories come back to her. She realizes that she was not alone throughout her childhood as she had thought. There was someone else who had always been with her. Rod concludes that this was Historia's elder half-sister, Frieda, and that she must have erased Historia's memories to protect her. Touching Eren must have returned them to her.
When Historia asks where Frieda is so she can thank her, Rod informs his daughter that she is no longer of this world. Five years ago, Grisha Jaeger killed Rod's wife and five of his children, including Frieda. Grisha possessed the Power of the Titans and came to the Underground Chapel to steal the power of the Reiss family that resided in Frieda.
Frieda should have been able to defeat Grisha with her Titan, due to its superior ability, but she was not experienced in using it. She was eaten by Grisha, who stole her power. Grisha then stamped out and killed the remainder of the Reiss family. Only Rod escaped alive.
Historia asks her father why Grisha would do such a thing when they are interrupted by Kenny Ackermann. Kenny informs them that a coup d'état happened and all regiments of the military have switched sides. The assembly has been captured and the public knows that the King is a fake. He suggests Rod wrap things up because the Scouts will be here soon. Rod understands and sends Kenny and his Anti-Personnel Control Squad to guard the entrance. Kenny obeys, but leaves with a derisive snort.
In Capital Mitras, Dhalis Zachary puts the finishing touches on his torture of Aurille. The noble is suspended upside-down, almost entirely naked, and informed that he will be digesting everything he eats from the bottom up thanks to a tube that runs from one end of his body to the other. Zachary also announces that he plans to parade Aurille in public like this once a week, to humiliate him in front of the people he once tyrannized. Uncowed, Aurille tells Zachary that his blood is "slave blood" and different from that of the nobles, so he will lose his memory soon.
Elsewhere, as Erwin Smith prepares the formerly imprisoned Scouts to depart, Dot Pyxis informs him that all the officials are saying the same thing as Aurille. The Reiss family must be able to alter memories as Erwin's father suspected. Only certain bloodlines are immune, which means that if Rod gets a hold of Eren's "Scream" the coup will amount to nothing.
Pyxis also tells Erwin that unlike him, he does not have a fondness for gambling. He values the number of remaining humans over his own life. The only reason he backed Erwin's plan is because he believes it is the better choice for humanity. He would have fought against Zachary, had the government been the superior choice. Realizing that his words are bleak following a successful coup, he asks about a song in which humans one day stop fighting.
One of the Scouts runs over to alert Erwin that they are ready. Before he leaves, Erwin tells Pyxis that humans will fight until humanity is one or less, causing Pyxis to laugh. Erwin then leads the Scouts towards the chapel in Reiss territory to rescue Eren and Historia.
As the bulk of the Scouts head out under Erwin's command, Squad Levi continues their journey to the chapel. Levi Ackermann warns his squad that Kenny will be their biggest obstacle and they should regard him as Levi's equal, or an even deadlier enemy given his gear. The squad expresses concerns about whether they can actually beat him, but Armin Arlelt thinks there is a possibility since training and combat experience are two different things.
Hange Zoë and Levi discuss Kenny's name, and he asks Mikasa Ackermann if Kenny might be a relative of hers. Mikasa says that she heard from her parents that the Ackermanns were once persecuted in the cities, but she never learned the reason. Her father did not seem to be a different race like her mother.
Levi asks her if she ever experienced a moment when she felt a power awaken in her, and Mikasa thinks back to when Eren was grabbed by one of her kidnappers. She picked up the knife in order to save both of them and something changed in her. Mikasa tells Levi that she has, and he explains that Kenny also had such a moment. Kenny had felt an absurd amount of strength surge through him and he knew exactly what to do. Levi has also had those moments.
In the cavern beneath the public chapel, Kenny remembers a conversation with his bedridden grandfather. His grandfather asked him if he was out killing Military Police again, which Kenny freely admitted. He let his grandfather know that a branch of the family had moved down near Shiganshina District, but someone had been interfering with their business so they were still poor. Kenny asked his grandfather why this was happening if they used to be warriors who protected the King.
His grandfather told him that they were not hated by the King so much as they were feared. The King's power would allow him to alter the memories of all of humanity, except for a few bloodlines. Among them, two turned their backs on the King, the Ackermanns and the Oriental clan. Kenny correctly concluded this was the reason for the persecution. He also informed his grandfather that he found his sister, Kuchel Ackermann, in a brothel and that she had gotten pregnant by one of her customers. She planned to keep the child.
Above ground in the publicly known chapel rebuilt by Rod Reiss, Hange, Levi, and his squad search the interior. They find a trapdoor under a rug that leads into the crystal cavern below where the Anti-Personnel Control Squad waits for them. Caven informs the soldiers with her that they should expect to face at least seven enemies, with Levi among them, and this time they will not have the advantage of an ambush. They cannot count on the other Interior Police or the government.
Caven reminds them of why they joined Kenny and sought meaning in lives they otherwise found meaningless, and asks them to continue trusting in Kenny and his dream.
Currently Publicly Available Information
Among those with the Power of the Titans, some have a special 'Scream.' While the Female Titan can use a 'Scream' to control Pure Titans, the royal family's Titan has a similar ability and is believed to possess the power to alter human memories as well.