|...It's not like I don't have regrets. But... we... did the right thing, didn't we? We stopped the Rumbling...|
|— Connie Springer after seeing the remains of the Founding Titan|
Mikasa Ackerman experiences a headache as Falco Grice lands at Fort Salta with the surviving Survey Corps and Warrior Unit soldiers on his back. The Rumbling appears to be over, but the centipede that emerged from the Founding Titan has survived and so has Eren Yeager. Reiner Braun moves to tackle the centipede while Armin Arlert holds off Eren. The centipede emits a gas that covers the fort and the Eldians around it. Recognizing the danger, Levi Ackerman gets Pieck Finger and Mikasa back on Falco so they can escape before the gas transforms all the other Eldians, including members of the Survey Corps and the Warriors' families into Titans.
The Titans join the centipede to fend off Reiner, who receives help from Pieck and Annie Leonhart. Meanwhile, Falco carries Mikasa and Levi towards Armin and Eren. Mikasa has a vision where she and Eren ran away from the war with Marley and he asks her to forget him when he dies in four years. In the real world, Mikasa decides that she will not forget him and directs Falco and Levi to take her to Eren and open a path through the mouth of his Titan. When Levi creates an opening, she lands inside and decapitates Eren while bidding him farewell.
The Rumbling has stopped and Falco Grice lands his Titan by the cliff on the outskirts of Fort Salta. As his passengers marvel at the collapse of Eren Yeager's Founding Titan, Mikasa Ackerman experiences a headache. She remembers Eren's story about the Ackerman clan experiencing headaches upon awakening and becoming slaves who followed orders. Despite the fact he said he hated her, she finds herself unwilling to accept that could be the last time they would ever meet.
Looking at the people outside the fort, Gabi Braun and Pieck Finger recognize and reunite with their parents. Falco joins his as well when he exits his Titan. As he stands with the other surviving members of the Survey Corps, Connie Springer admits he has regrets, but speculates that they did the right thing. After learning that her father was the one who led the Eldians of Liberio here, Annie Leonhart runs off to find him.
Gabi tells Karina Braun that Reiner is still fighting and the group, still at the edge of the cliff looks over it in search of Reiner and the shining centipede he was fighting. They see that he has survived, but so did the centipede. Armin Arlert's Colossus Titan climbs out of the crater formed by his transformation and follows Reiner towards the centipede, which is now by the base of the cliff.
Behind Armin, the light of a Titan transformation flashes and Eren's new Titan appears; skinless and as tall as the Colossus. The survivors on the cliff realize that Eren cannot be allowed to come into contact with the centipede and they will have to kill it or Eren. Pieck and Falco say farewell to their parents in preparation for one last mission. Mikasa clutches her throbbing head as she wonders how things turned out this way.
As Reiner approaches the centipede it emits gas from pores in its body. The gas rises up over the cliff and sweeps over the fort and the people around it. People are confused, with Mikasa wondering if it died, but Connie is the one who figures out that it is similar to the gas used to transform the people of Ragako village.
Recognizing the danger, Levi Ackerman orders Mikasa and Pieck to climb on Falco, who is still connected to his Titan. The four of them are immune to the gas since they are either Ackermans or have the power of the Titans. Falco carries them aloft, though Pieck has to be held by Mikasa because she does not want to leave her father.
Jean Kirstein and Connie watch them go, entrusting them with the rest, as previous members of the Survey Corps had done. Connie asks Jean if he remembers the night of their entrance ceremony, and good-naturely blames him for getting them stuck with the job of saving the world.
A moment later, all the Eldians in the vicinity of Fort Salta are transformed into Titans. They careen off the edge of the cliff and rush to the centipede. Despite the fact it has summoned reinforcements, Reiner steels himself to prevent it from reaching Eren. Behind him, Armin faces Eren and the two gigantic Titans grapple.
Reiner wrestles with the centipede, and to his horror, he recognizes some of the faces of the Titans around him. As Falco dives towards the fray, Pieck jumps off his back and transforms, biting on to the head of the centipede. Annie arrives as well, attempting to pull the centipede back.
As Falco flies towards Armin and Eren, Mikasa's headache intensifies. Levi tries to get her to stay aware of her surroundings since they are the only ones left who can kill Eren, but she does not think she can take any more of it and wishes she was back home.
Mikasa is sleeping, when she feels a hand on her shoulder and a voice telling her to wake up. She opens her eyes to see a concerned Eren telling her that she will catch a cold. For a moment she is confused and asks when she fell asleep. She thinks she must have had a long dream. Eren notices that she is crying and she does not know why. She wonders if it is okay for her to be here.
Eren tells her there is nothing they can do about it now. They ran away from the war with Marley and it has been two months since it ended. The war to invade Paradis Island will start soon. Eren concludes that running away is the only way to survive. He could not condemn Historia Reiss or commit genocide against the people outside the Walls so he should live out the last four years of his life in peace with Mikasa. She was the one to suggest it.
Mikasa smiles and Eren asks her for one last promise: to throw out her scarf and forget about him once he is dead. She has a long life ahead of her. Marks appear on his cheeks as if he has been inside a Titan.
Outside of Mikasa's vision, the battle is going poorly. Armin is battered by Eren, and Reiner and Annie are being overwhelmed. Mikasa reaches in her shirt and pulls out her scarf. She wraps it around her neck and apologizes to Eren, saying that she cannot forget him. Mikasa tells Levi and Falco that Eren is in his Titan's mouth and to back her up. She will finish the job.
Just after Eren punches through the Colossus Titan's head, Levi shoots a Thunder Spear into the teeth of Eren's Titan, creating an opening barely large enough for a person to fly through. Mikasa lands inside, blade drawn, and spots Eren's head on the end of a long spine. She swings her blade, severing his head from the spine.
In the vision, Eren sits on a bench as though he has gone to sleep. She cradles his head and tells him she will see him later. In the real world, she kisses him farewell as Ymir Fritz looks on and smiles.