Berserk Button: Frieda (while under the influence of the First King's ideology) going on and on about how Eldians deserve their fate because of their ancestors' crimes serves as this to Eren.
Eviler than Thou: Although Zeke attempts to convince Eren to his side, he instead finds out that Eren's own ideals were far worse than he ever thought.
Loving a Shadow: Zeke provides a familial, rather than romantic, version of this trope; he always assumed Eren was also a victim of Grisha's brainwashing like he was in the past, and always idealized himself saving him from their father's control. This is lampshaded by Eren:
Eren: The pitiful younger brother you're looking for doesn't exist.
Not Brainwashed: Zeke believes that Eren has been brainwashed by their fathers ideals into embracing the same Nationalistic mindset Grisha forced upon him. As such he takes Eren through Grisha's memories in order to turn him to his side. Eren however makes clear that he has never been manipulated by anyone, everything he's done has been by his own choice.
Eren: If someone tries to steal my freedom away from me, I steal theirs first. Our father never taught me that. I've been that way since birth.
Eren: The pitiful younger brother you're looking for doesn't exist. Neither does the younger brother who shares the same wound as you. What I see here is a man who doesn't know any other way to define himself beside continuing to deny his father's wish to restore Eldia.
The Attack Titan can see into the future...and in turn, that future can influence past wielders.
Eren has been manipulating his father from the future this whole time.
Seers: It's revealed that this is a unique ability that the Attack Titan possesses: the holders of this Titan can have access to memories of it's future holders, and Grisha is able to see that he will successfully steal the Founding Titan from Frieda.
Stable Time Loop: At first, Zeke thinks Grisha somehow changed the past. Then he realizes Eren was the only reason why Grisha was able to bring himself to take the Founding Titan and murder the Reiss family. Eren knew he had created a time loop all along.
Wham Episode: With the reveal of the Attack Titan's powers and Eren's influence on Grisha from the future, Eren secures his place as the Big Bad.
Whole Episode Flashback: Played with. Zeke and Eren visit Grisha's memories since the moment Eren was born until he kills the Reiss family, and Zeke, as well as the audience, discover that the events of Frieda and her mother and siblings' deaths didn't occur exacty as Rod had told them and the way Eren remembered when he accessed his father's memories: it was actually Eren's present self that tampered with the timeline and influenced his father to kill Frieda and take the Founding Titan, killing the rest of the Reiss family in the process. Grisha actually didn't want to kill them and is visibly distraught after the deed is done.
