|There are people I want to bring back, too. Hundreds of them. I've had to say farewell since the day I joined the Scouts. ... But... You know, don't you? No matter who it is, there comes a day to say farewell.|
|— Hange Zoë consoling a distraught Mikasa Ackermann|
Zeke tells Eren Jaeger that someday he will come back to rescue him. Eren then realizes that Zeke strongly resembles his father, Grisha. Levi Ackermann arrives to pursue Zeke with Eren's remaining weapons, when Eren suddenly realizes that Armin Arlelt is breathing. Eren asks Levi for the Titan injection so they can save Armin by having him eat the incapacitated Bertholdt Hoover. However, Floch arrives with a dying Erwin Smith and request that the injection be used on Erwin.
After losing Reiner Braun to the Cart Titan, Hange Zoë and the rest of Levi Squad arrive to find Eren and Mikasa Ackermann struggling with Levi for the injection, either with words or by force. Hange eventually manages to talk down Mikasa and Levi has everyone clear out so he can use the injection on Erwin. However, when Erwin begins muttering a childhood memory, Levi decides it would be kinder to let him pass on. He gives the injection to Armin who eats Bertholdt and emerges from his Pure Titan as his friends gather around.
Eren Jaeger stands momentarily speechless over the burned body of his childhood friend, Armin Arlelt. He realizes he should have known what would happen, but had no choice but to rely on him. Eren hears the weight of a Titan landing in the distance, and turns around in time to see the Cart Titan, carrying Zeke on its back.
The Cart Titan gallops across the rooftops to reach Eren, who quickly moves to hold the unconscious Bertholdt Hoover hostage, placing his blade at the Warrior's throat. As the Cart Titan stops, Eren gets a better look at Zeke and sees that he has marks around his face that show he can turn into a Titan. He realizes that he is probably the Beast Titan.
Zeke looks at Eren in shock and asks if he is Eren Jaeger. He says Eren looks nothing like his father and tells him that he knows what Eren is going through, as they are both victims of Grisha Jaeger. As Zeke tells Eren that he has been brainwashed by his father, Eren realizes that Zeke resembles Grisha.
However, Zeke looks up with consternation when he sees that Levi Ackermann has survived his battle with the remaining Titans and has climbed to the top of Wall Maria. Being in no shape to fight him again, Zeke calls their fight a draw and apologizes to the unconscious Bertholdt, saying that it is the end for him. The Cart Titan turns to leave and Zeke tells Eren that one day he will be coming back to rescue him. The Cart Titan gallops away with Zeke in tow.
Levi lands on the rooftop near Eren after using the last of his gas. He demands the rest of Eren's blades and gas so he can pursue Zeke. Eren begins to comply when he hears Armin gasp for breath.
Elsewhere in Shiganshina District, Hange Zoë asks a conscious, but dismembered, Reiner Braun about a metal case that was in his chest pocket. He tells her that it is a letter written by Ymir, and that the Scouts need to deliver it to Christa. Hange agrees, but only after they inspect it. She would like to ask him more questions, but draws her blade, feeling that he is not inclined to talk. Reiner does not disagree.
However, when Hange begins to cut Reiner's throat, Jean Kirschtein asks her to wait, thinking they might be able to steal his power. Prior to beginning the operation, Erwin Smith had laid out guidelines for the use of the Scout Regiment's one syringe of Titan injection, with the expectation that they could possibly take the Beast, Armored, or Colossal Titan's powers. Not only could the Scouts gain valuable information regarding Titan powers, but they could revive a single soldier on the brink of death.
However, Hange does not feel that all the conditions have been met. Levi has the injection, but they do not know his status and she is not certain they have the time to find out. Even if she cuts off Reiner's head, she is not certain that will actually kill him. Jean argues though, that this is not like her, and asks how they are supposed to beat the Titans if they back down because they lack the knowledge. Hange considers and asks Mikasa Ackermann to meet up with Eren and Armin to check out their situation, then to refill her gas and retrieve the injection from Levi. If she cannot, then she is to fire a signal flare as a signal to end Reiner. Mikasa agrees and flies off to find Levi.
Mikasa arrives to find Eren bent over Armin, desperately encouraging his friend to breathe. Eren hurriedly asks Levi for the syringe so they can have Armin eat Bertholdt. Levi, after a moment's hesitation, agrees and pulls out the case with the injection. Seeing this, Mikasa fires a signal flare as directed, but before Hange can kill Reiner, the Cart Titan gallops up behind her. Jean quickly fires his omni-directional mobility gear and pulls her out of the way before the Cart Titan can eat her.
Hange gets back up in time to see that the Cart Titan has picked up Reiner in its mouth, and it runs away with him and Zeke. Jean curses and blames himself for intervening when Hange was about to kill Reiner, but she reminds him that ultimately she made the call. She decides that they should regroup with the others.
As Levi is about to hand Eren the Titan injection, Floch climbs up on the rooftop, carrying Erwin on his back. Erwin is severely wounded, but still alive, and Floch has been looking for Levi in hopes that the injection could save him. Seeing this, Levi takes back the injection and has Floch bring Erwin onto the roof. Levi inspects and confirms that Erwin is still breathing, so he announces that Erwin will receive the injection. Eren is horrified, reminding Levi that he had already agreed to use it on Armin. Levi responds that he will revive the one who can save humanity. He hears a blade being drawn and turns to see that Mikasa has drawn her weapon, tears in her eyes.
On the Wall, Zeke surveys the wasteland of Shiganshina and notes that Reiner was incredibly lucky to have survived.
Realizing what Eren and Mikasa intend, Levi asks them if they understand what they are doing. He reminds them that Erwin is their commander, and to stay out of his way. Eren grabs onto the serum in Levi's hand, and Levi orders him to keep his emotions in check. Eren furiously asks why Levi did not use the serum on Armin right away. Levi admits that he was considering the possibility of Erwin still being alive, and now that Erwin is here, he will receive the injection. Eren tightens his grip on the Titan injection, and Levi, losing his patience, strikes Eren with his fist, knocking out several of his teeth and sending him flying. Outraged, Mikasa lunges at Levi and puts her blade to his throat. She realizes that Levi has been weakened from his previous battles, and she is certain she can take the injection from him by force.
Both Levi and Floch appeal to her sense of reason and the need to save Erwin so they can use his talents to save humanity. Though Eren is barely able to speak, he counters that it would be no different if they lose Armin. Armin discovered Annie Leonhart's identity as the Female Titan, he was the one who came up with the plan to save Trost and thought of moving soldiers at night, and it was thanks to Armin that they found Reiner and defeated Bertholdt. Eren believes that Armin will be the one who will save them, not Erwin or even Eren himself.
Mikasa renews her efforts to take the injection from Levi, but Floch stands up to her, saying that she is not the only one who has had it rough. Floch lets her know that all of the Scouts that were on the other side of the Wall are dead, killed by the Beast Titan's barrage. Erwin came up with a plan to fight back against the Beast Titan, and Floch's comrades were all slaughtered just as planned. When Floch found Erwin, he thought about killing him, but decided that would have been too easy. He wants Erwin to endure more of this hell. It takes a devil to fight the Titans, and Floch believes he was spared when he should have died so that he could bring Erwin back.
Floch tries to take the injection and Mikasa moves to intercept him, but Hange grabs her first and manages to pull her away before she can strike him. The rest of the squad has arrived now, and is able to see the choice that must be made. Levi gets up and opens the injection case, preparing to inject Erwin. Mikasa screams and Hange reminds her of how much they need Erwin and that she knows what it is like to lose people. She is only here now because Moblit Berner had died pushing her into a well to escape the Colossal Titan's transformation blast. Though there are countless people Hange wants to bring back, there comes a time to say farewell, and they have no choice but to keep moving forward.
Hearing this, Mikasa finally relents and Levi prepares the injection. However, Eren weakly pulls at Levi's leg and asks him if he knows about the sea. Despite Floch's intervention, Eren tells Levi about Armin's dream to look at the sea, and admits that, though he was only ever driven by hatred of the Titans, Armin is not like him, and has dreams of his own. Levi glances at Armin's body and then gives the order for everyone to clear out so he can have Erwin eat Bertholdt. The group relocates, with Floch taking Eren away so he cannot intervene, and Levi is left alone.
Levi drags Bertholdt into position as he thinks about Erwin and Armin's respective dreams. He takes Erwin's arm and prepares to give him the injection when Erwin suddenly lifts it out of his grip and raises his hand, apparently believing himself to be back in his father's classroom. Delirious, Erwin asks his father how they can know for sure that there are no more humans outside the Walls. Levi regards him with surprise and remembers how he asked Erwin to give up on his dream, and how his uncle Kenny Ackermann had spoken about how people could only keep going if they were drunk on something. Remembering Erwin's gratitude to him, Levi makes his choice.
Bertholdt wakes up in time to see a small blond Titan looming over him. He begins to struggle and notices his former friends watching from several rooftops away. Bertholdt panics and cries out for help, but to no avail. As he screams for Annie and Reiner, Armin's Titan closes its jaws on his head and devours him.
Floch asks Levi why he changed his mind as Levi and Hange sit beside Erwin's body. Levi explains that Erwin only became a devil because that was what was needed of him. He had been set free, but they were about to drag him back, and Levi decided it was time to let him rest. Levi apologizes to Erwin that he was not able to kill the Beast Titan like he promised, so he will have to wait. Hange inspects Erwin and lets Levi know that he has passed away.
Behind them, the blond Titan collapses to the ground. Eren, Mikasa and the other 104th cadets surround it as Armin Arlelt emerges from the Titan, unharmed.
Currently Publicly Available Information
Not only can Titan powers and much-needed information be stolen by using the injection, but it also allows the revival of someone who is critically wounded. The ideal candidate would be someone near death that is already close to an incapacitated enemy with Titan powers.