|We shot our officers upon orders from Zeke Yeager. We are the Anti-Marleyan Volunteers. Our goal...is to free the Eldian people.|
|— Yelena and Onyankopon to Hange Zoë and Levi Ackerman|
Armin recalls how Paradis Island encountered the first of many ships sent from Marley and how the island decided to form an alliance with Yelena and Zeke Yeager to fight Marley. The two sides begin to pool their resources to bring the fight to Marley as they seize the many warships sent to Paradis Island.
He talks to the crystal holding Annie about how they buried their lost comrades and mentions Sasha's death, wishing a peaceful option was available instead of always having to fight; elsewhere, Eren, who is slowly becoming numb to the death and violence around him, resolves to continue fighting Paradis Island's enemies to the very end.
Holding onto a seashell, Armin recounts events from three years ago to an unknown listener. At that time, a Marleyan scouting vessel approaches Paradis Island, preparing for landing. The captain resolves to inform Marley of the island's situation, when suddenly, the Attack Titan bursts up from under the surface of the ocean, lifting the ship up before bringing it crashing down on the shore. Hange delivers an overly enthusiastic welcome to the cowering soldiers, inviting them to the island for tea as distinguished guests. Then, she and Levi bring in a captured soldier, from the vessel's advanced party, who begs his captain to shoot the two.
The captain refuses to listen to Hange and berates them as devils; Hange then reminds him of Eren's Titan standing behind him and asks how he plans on escaping. Refusing to yield to the islanders, the captain raises his weapon when suddenly, a shot rings out. Everyone is in shock as the captain falls over dead. Yelena, his killer, along with Onyankopon, order the others to surrender their weapons, before accepting a bewildered Hange's invitation to come ashore for a cup of tea. She then stares at Eren's Titan and says she had been wanting to meet him for quite some time.
As the members of the Survey Corps look from afar, they wonder who the woman is and if they can trust them. Eren admits that they were lucky he was able to obstruct the ship from landing, because Marley's full naval force would easily be able to beat them. Inside the tent, Hange is amazed by the weapons Yelena and Onyankopon have with them; they reply it is standard equipment for Marleyan soldiers and inform Hange and Levi they have roughly one million soldiers and three fleets containing twenty-one battleships. They both admit that Marley is capable to attack from the air as well; a shocked Hange asks why they have yet to come and destroy Paradis Island if they have this capability. Yelena responds that Marley has many enemies, and they considered Eldia to mainly stay contained by the Titans, expressing amazement when Levi makes an offhand remark that the Eldians were able to kill all the Titans on the island. When Hange theorizes the two are spies who infiltrated Marley's military, Yelena admits they were forced in but were given a purpose by Zeke Yeager when he managed to show them hope.
At an assembly gathered between the heads of the military, Hange gives Zeke's demands in return for him helping the Eldians; sharing technology for weapons, starting relations between Paradis Island and other warring nations fighting Marley, and provide support. When several members of the military object due to Zeke being their primary enemy for so long, Darius Zackly muses that they would not easily switch to peaceful talks after such a long time at war. However, Dot Pixis advises they listen to all the terms before ultimately deciding what to do.
When Zeke's secret plan is mentioned (which involves Eren's possession of the Founding Titan and a Titan possessing royal blood), Eren admits that it is true and recalls his encounter with Dina Fritz's Titan and how he was able to control pure Titans for a brief period of time. When Levi asks why Eren had stayed silent about this, Eren admits it was for Historia's safety due to being unreliable information at the time; despite Hange and Levi's disappointment in Eren's decision, Hange admits it does fall in line with Zeke's plan. Nile Dok is still against it, with other members of the Military Police chiming in and calling for Yelena's death due to her not being trustworthy; Hange insists they need her forces and technology to help them.
Later, Yelena uses her wireless communication to come in contact with the second Marleyan survey fleet heading towards the island. As the fleet approaches, Armin and two other Survey Corps soldiers lie in wait behind a rock in a boat. As three Marleyan rescue boats attempt to approach the fleet, Armin transforms into his Colossus Titan. The crew who are shocked, panicked and cornered are forced to dive overboard and swim to shore where they are met by Levi and other Survey Corps who point guns at them and take them as prisoners. Over the next few years, both Armin's Colossus Titan or Eren's Attack Titan aid in capturing or destroying Marleyan ships when they approach the shore of the island.
As the two sides share advancements and train, Eren is at a shooting-range with both Armin and Mikasa; Armin states both sides are getting to know each other and the harbor will be completed soon, so they can travel across the ocean. Eren then asks Armin if he can see anything useful in Bertolt's memories while reflecting that his half brother only has three years left to live. Armin says there is nothing of use he could see and sadly reflects that this course of action will result in more deaths and hoped there was a peaceful way to clear the misunderstandings; Eren retorts the rest of the world still views them as monsters and the Marley soldiers glare at their walls in contempt. He reaffirms his belief that to buy them time, Paradis Island needs to do something to ensure there is no interference.
Back in the present, the airship returns back to Paradis Island and the survivors prepare to bury the deceased, including Sasha. Meanwhile, the Military Police transfer Gabi and Falco into custody. All those present share sorrowful looks, except for Eren who merely walks away. Armin admits that, despite intending to understand Eren more than anyone else (even Mikasa), he does not truly know Eren anymore. Both sides have now suffered the same fate; total destruction by an enemy force attacking their homeland and countless deaths. Knowing that Marley will retaliate soon, Armin admits their path to reconciliation has been cut off despite not having any other choice. He looks up at the unknown person and it is shown to be Annie Leonhart, still encased within her hardened crystal. Armin begs Annie to respond in some way.
Outside, Zeke bemusedly states to Levi that the citizens of Paradis Island are calling it a victory despite not knowing anything. Levi merely states to Zeke that he will send Zeke back to Marley in pieces and is content to wait until his secret plan goes into effect. Zeke gives his thanks and asks if he is going to see Eren soon, noting that Levi is still glaring at him. Mikasa leans on a tombstone, looking to the future, noting that Paradis Island and the Eldians will survive if they fight. In a separate location, Eren washes himself while echoing the same statement, resolving to fight and fight some more in order to win the upcoming battles.