Isayama planted clues from chapter 1 onward. On the left, the clue; on the right, its payoff (hidden according to your spoiler level).
Chapter 1 is titled “To You, in 2,000 Years”, a title that seems unrelated to the story.
Chapter 122 is titled “From You, 2,000 Years Ago”: the first addresses Ymir Fritz from the present, and Eren speaks to her in the Paths about 2,000 years after she obtained the power of the Titans.
Characters: Eren Yeager, Ymir FritzHidden character
Eren wakes up crying under a tree after a long dream, and asks Mikasa why her hair is so long, even though it's short.
It was a memory of the future transmitted through the Paths: an adult Mikasa, with long hair, says goodbye to him with “See you later, Eren.” The ending shows the scene connects to the moment Mikasa makes her choice and to the tree where she buries him.
Characters: Eren Yeager, Mikasa Ackerman
Grisha always wears a key around his neck and promises to show Eren the basement of their house when he returns.
The basement holds Grisha's journals and photographs revealing that humanity exists beyond the Walls, along with Marley and the truth about the Eldians.
Characters: Grisha Yeager, Eren Yeager
In a blurry memory, Grisha injects Eren with something in a forest during the fall of Shiganshina.
It was Titan serum: the transformed Eren devoured his own father and inherited the Attack Titan and the Founding Titan.
Characters: Grisha Yeager, Eren Yeager
The Smiling Titan devours Carla while ignoring other humans, and Hannes flees with the children.
The Smiling Titan was Dina Fritz, Grisha's first wife and Zeke's mother.
Characters: Dina FritzHidden character, Carla Yeager, Grisha Yeager
The Smiling Titan heads straight for the Yeager house, as if it knew where to go.
It is revealed that Dina walked right past Bertholdt: Eren, with the Founding Titan's power, steered her toward his mother so that everything would happen as he had seen it.
Characters: Eren Yeager, Dina FritzHidden character, Bertolt Hoover, Carla Yeager
Annie has mastered a unique hand-to-hand combat style learned from her father, and takes down Eren and Reiner in training.
The Female Titan uses exactly those techniques; Armin and Eren identify Annie as its holder.
Characters: Annie Leonhart, Eren Yeager, Reiner Braun
The Female Titan protects her nape by hardening her hand and heads straight for Eren during the expedition.
Annie has mastered hardening and is hunting for the “Coordinate”; in the end she encases herself in an unbreakable crystal.
Characters: Annie Leonhart, Eren Yeager
Annie complains that her ODM gear belongs to someone else, and she is using the gear of Marco, who died in Trost.
Annie, Reiner and Bertholdt took Marco's gear and left him to die; Annie also killed Hange's Titans, Sonny and Bean.
Characters: Annie Leonhart, Marco Bott, Reiner Braun, Bertolt Hoover
At Utgard Castle, Ymir easily reads the label on a can of herring written in a language no one else understands; Reiner notices.
Ymir came from Marley: she was a mainland Eldian turned into a Pure Titan, who devoured Marcel and took the Jaw Titan.
Characters: Ymir, Marcel GalliardHidden character
On the first expedition, a faceless Titan is seen inside Wall Rose, revealed when part of the wall crumbles away.
The Walls are made of millions of Colossal Titans; released by Eren, they begin the Rumbling.
Characters: Eren Yeager, Hange Zoë
Pastor Nick refuses to reveal the secret of the Titan in the wall and alludes to a family that knows everything.
The Reiss family is the true royal family and holds the power of the Founding Titan.
Characters: Rod ReissHidden character, Historia ReissKrista Lenz, Hange Zoë
Connie finds a Titan lying on top of his house in his village, unable to move, with no trace of the villagers.
The Titan mutters “welcome home” and has his mother's face: the villagers of Ragako were turned into Titans by Zeke, and Pure Titans are Eldians.
Characters: Connie Springer, Zeke YeagerHidden character
Reiner and Bertholdt talk to each other as if they were soldiers and Warriors at once; Reiner mentions going back “home” several times.
Reiner suffered from a personality split between the Paradis soldier and the Marleyan Warrior.
Characters: Reiner Braun, Bertolt Hoover
Mikasa suffers severe headaches at key moments and feels a power awaken when she decides to fight.
Her strength comes from the Ackerman clan, a lineage modified by the Titans. The headaches are linked to Ymir Fritz, who was watching Mikasa.
Characters: Mikasa Ackerman, Ymir FritzHidden character
Mikasa has a tattoo inherited from her mother, a crest on her wrist.
It is the crest of the Azumabito clan of Hizuru; Kiyomi recognizes her as its heir.
Characters: Mikasa Ackerman, Kiyomi AzumabitoHidden character
Kenny and Levi share superhuman strength; Kenny refers to “us Ackermans.”
Kenny is Levi's uncle, and both belong to the Ackerman clan, like Mikasa.
Characters: Kenny AckermanHidden character, Levi AckermanLevi, Mikasa Ackerman
Eren punches the Smiling Titan's hand and, after his scream, the Pure Titans swarm that Titan and the Armored Titan.
Contact with a Titan of royal blood (Dina) activated the Founding Titan's power in Eren.
Characters: Eren Yeager, Dina FritzHidden character
The Beast Titan can speak and controls the Pure Titans with a scream.
Zeke has royal blood; his spinal fluid turns Eldians into Titans, and he can control them with a scream.
Characters: Zeke YeagerHidden character
Kruger mentions Mikasa and Armin in his conversation with Grisha, even though they shouldn't exist yet.
The Attack Titan can see the memories of future holders; Kruger saw Eren's.
Characters: Eren KrugerHidden character, Grisha Yeager, Eren Yeager
When he kisses Historia's hand at the medal ceremony, Eren has a strange reaction and goes into shock.
Touching her, he saw memories of the future, including the Rumbling, which explains his later change.
Characters: Eren Yeager, Historia ReissKrista Lenz
Facing the sea, Eren points at the horizon and asks whether they'll be free if they kill all the enemies on the other side.
Eren plans to destroy the outside world with the Rumbling.
Characters: Eren Yeager, Armin Arlert
Marley uses wine as a gift to the Paradis soldiers after the volunteers arrive.
The wine contains Zeke's spinal fluid: anyone who drank it can be turned into a Titan by his scream.
Characters: Zeke YeagerHidden character, YelenaHidden character, Dot Pixis
Falco says he wants to fly like a bird and repeatedly appears surrounded by birds.
After inheriting the Jaw Titan from Porco with Zeke's fluid in his body, Falco develops a Titan capable of flight.
Characters: Falco GriceHidden character, Porco GalliardHidden character, Zeke YeagerHidden character
Armin often visits Annie's crystal and admits that part of what he feels comes from Bertholdt's memories.
Annie, freed from the crystal, confesses she heard Armin's visits and joins him in the final battle.
Characters: Armin Arlert, Bertolt Hoover, Annie Leonhart
Ymir Fritz remains trapped and obeys King Fritz even after death, building for 2,000 years.
Ymir loved King Fritz and was waiting for someone to break that love; Mikasa, by killing Eren, whom she loves, shows her how to free herself.
Characters: Ymir FritzHidden character, Mikasa Ackerman, Eren Yeager
In the opening pages, Eren lies beneath the tree on the hill outside Shiganshina.
Mikasa buries Eren's head under that tree, which over the years grows to resemble the tree where Ymir found the source of the Titans.
Characters: Eren Yeager, Mikasa Ackerman, Ymir FritzHidden character
A bird appears in key scenes involving Eren and freedom.
After Eren's death, a bird wraps Mikasa's scarf around her, alluding to him.
Characters: Eren Yeager, Mikasa Ackerman
Erwin recounts that his father was killed for questioning the official history of the Walls.
The royal family had erased the inhabitants' memories; the basement confirms Erwin's father's theory.
Characters: Erwin Smith
Ymir seems to know Reiner and Bertholdt before their identities are revealed, and knows the Titans aren't what they seem.
Ymir ate Marcel, Reiner and Bertholdt's comrade, and inherited the Jaw Titan.
Characters: Ymir, Reiner Braun, Bertolt Hoover, Marcel GalliardHidden character
Historia is treated as someone who must hide her surname and origins.
Historia is the illegitimate daughter of Rod Reiss, heir to the royal family, and becomes queen.
Characters: Historia ReissKrista Lenz, Rod ReissHidden character
Zeke recognizes Mike's ODM gear and shows interest in talking with humans from within the Walls.
Zeke is Eren's older half-brother and Grisha's son, raised in Marley.
Characters: Zeke YeagerHidden character, Mike Zacharias, Eren Yeager
Sasha decides to save Kaya and teach her to defend herself, questioning how to act.
Kaya and the Braus family take in Gabi and Falco after Sasha's death, showing that the cycle of hatred can be broken.
Characters: Sasha Braus, Gabi BraunHidden character, Falco GriceHidden character
Eren tells Armin that someday they'll see the sea and the “outside world.”
When they reach the sea, Eren doesn't feel the joy he expected and realizes there are enemies on the other side.
Characters: Eren Yeager, Armin Arlert
The Colossal Titan appears out of nowhere in Shiganshina and Trost, without anyone seeing where it comes from.
Bertholdt is the Colossal Titan; Reiner is the Armored Titan.
Characters: Bertolt Hoover, Reiner Braun