Warning: this article contains spoilers for Attack on Titan.
A flashback in Attack on Titan episode 87 shows Eren and his friends when they were once happy, and this is a reminder of what Eren is fighting for. Episode 87 is the final episode of Attack on Titan season 4, part 2. Before the episode's release, it was announced that the anime will conclude with season 4, part 3, titled "The Final Arc." In a season of infighting between the main cast, Attack on Titan episode 87 highlights who and what Eren is fighting for.
Attack on Titan season 4 pits a major conflict between Eren and his childhood friends, Mikasa and Armin. Eren plots to exterminate all life outside Paradis Island after he gains the power of the Founding Titan. However, he keeps his schemes secret from the rest of the Scouts, whom he considers his closest allies throughout most of the anime. Eren's Rumbling is already extinguishing life on foreign soil and has destroyed the last great naval resistance of humanity. It appears that the only people who can stop Eren are the ones who love him most.
The flashback to the Scouts' first trip to Marley serves as a timely reminder of their bond after all the bloodshed of Attack on Titan season 4. It depicts the characters in their natural states, rather than in situations where they must fight to survive. They're hopeful; they drink and laugh together like the friends they are. Eren does not forget this, as in another flashback when he talks to Zeke long after the Marley trip, saying, "I want them to live and be happy," even after he is gone. Attack on Titan episode 87 offers a reminder that even if Eren is now the anime's biggest villain, his motivations are grounded in his love for his friends, something most viewers can empathize with.
During the trip to Marley, the scene where Eren and his friends drink until they pass out reflects on what has been lost because of Eren's strategies and what can still be lost. The scene includes Sasha Braus, who died in the Scouts' attempts to help Eren when he attacked Liberio. Sasha epitomizes the sense of wonder that the Scouts felt when they reached Marley. She is distracted by a car and fascinated by ice cream, in awe of the world outside the walls. The sense of adventure she exhibited was also present in Eren before he learned the truth about the other continents. The death of Sasha in Attack on Titan is made more poignant by episode 87 and reminds viewers that she may not be the last one to die in Eren's extermination plan. The fact that the Scouts drink with refugees from the Marley Mid-East War also demonstrates their capability to be friendly towards people who do not share their place of birth or language.
Nonetheless, the possibility of peace with outsiders is no longer an option for Eren. The Marley trip demonstrates that, when detached from the cruelty of the world, the main cast from Paradis has the potential to live happy and simple lives. Due to Eren's comment to Zeke, it is clear that Eren remembers this. His motivation to protect his friends is only exacerbated by the fact that he only has a few years left to live. Eren believes that only he, in his last years, can end "the cycle of revenge fuelled by hate" and save his friends from more tragedy. The shining images that Eren sees of his friends' younger selves eating and joking portray the fondness he holds in his mind for those memories. Eren's conversation with Historia suggests that Eren is aware that his friends will also oppose his plan and that's why he must do it alone — to separate them from Attack on Titan's final conflict and to leave them as the only ones who remain.