The Paths are a place where past, present, and future intersect, but Zeke is content to use a trip down memory lane to show his little brother how their father Grisha “brainwashed” him into becoming a Restorationist. But things don’t go how Zeke plans, as he ends up learning more about Grisha that complicates his long-standing feelings of resentment stemming from his dad abandoning him and starting a new family.
We learn that Grisha found the Reiss family’s underground chapel years earlier than we thought, but chose instead to delay his mission so Eren could have a normal childhood. It’s here, in Grisha’s basement, where Zeke learns his dad didn’t forget him, keeping a photo of him and his mother close by. It’s also where we learn Zeke and Eren aren’t merely invisible observers, as Grisha senses Zeke’s presence but assumes he’s only dreaming.
As Eren stands by patiently, Zeke learns that Eren was never actually brainwashed. When Eren saved Mikasa and killed the monsters in human skin, he was being the same Eren Yeager he always was: neither a weak nor convenient little brother Zeke could use to facilitate his plans or share his scars. Even so, Zeke is determined to “save” Eren (i.e. get him to come around to his thinking) before he saves the world, which he says he can do at any time.
The harrowing incident Eren experienced with Mikasa eventually led to him telling her he wanted to join the Scout Regiment, which Mikasa relays to their parents. Eren doesn’t just want to protect those he loves, but wants to know what lies beyond the walls. Carla pleads with Grisha to discourage their son from taking this path, but Grisha knows there’s no stopping “human curiosity.”
In a return to the truly creepy underground chapel, Zeke and Eren watch Grisha try to convince Frieda to let him use the power of the Founder to protect the people in the walls from the Titans beyond it. Grisha even tells Frieda something she doesn’t know: that the Attack Titan within him can see into the future by having access to the memories of its future inheritors. But when it’s time for Grisha to eat Frieda and kill her family, he can’t do it. At least not until Eren whispers into his ear, reminding him what he’s come to do … and why.
Zeke may have the Founder Titan, but like Frieda, he’s unable to see the future like Eren can. This is why Grisha, after he kills the Reisses and gains the Founder, warns Zeke that things are ultimately going to go Eren’s way, not Zeke’s. He knows this because he’s already seen Eren’s memories of that future. All he can offer Zeke is a hug, his tears, and the affirmation Zeke always sought deep down: that he was loved and not forgotten by Grisha.
Following that cathartic embrace, Eren and Zeke return to the uncanny land of the Paths, and while Eren is still chained to the ground, he doesn’t seem the least bit concerned. Why would he? He knows the future, and if Eren has anything to say about it, it won’t involve the euthanization of the Eldians.