|I'll inherit the Beast Titan. Not for Marley, but to retake the Founding Titan and save the world. I'll free the world from the terror of Titans and free all Eldians from suffering!|
|— Zeke Jaeger's resolve about euthanizing Eldians|
Zeke Jaeger recalls his childhood and how he was forced to become part of his parents' plan to free Eldia from Marley. He becomes friends with Tom Xaver, a member of the Titan research team and vows to inherit the Beast Titan from him. He goes on to say he will ensure the success of the plan to take back the Founding Titan. After recalling his memories, Zeke triggers the Thunder Spear, detonating it and catching Levi Ackermann by surprise.
Grisha Jaeger and Dina Fritz take their young son Zeke atop one of the towers outside the Liberio internment zone and show him the city they live in. Grisha tells Zeke that as Eldians they are forced to live their lives inside what amounts as a birdcage instead of being able to see the rest of the world, and asks him if he would not like to leave that place, with Zeke replying that he does.
They are then found by a maintenance man who douses them in water upon seeing their armbands, reproaching them for the Eldians' alleged past crimes and telling them that they should have been exterminated instead of giving birth to more children. As they walk through the streets, amidst more hostility from the Marleyan citizens, Grisha hugs his son and tells him that the outside world is like this, and if he cannot stand it, he is going to have to change it.
The newest batch of Warrior candidates are seen training while two men watch from afar. One of them, Tom Xaver, asks if his successor will be among them. After noticing Zeke trailing behind the others, the other man, Theo Magath, comments that he does not seem to have the guts to be a Warrior.
After the training, Zeke is taken to his grandparents by his mother and father, who ask him how his training went. He admits it was really tough, but they are confident that he can become a Warrior, since he has a special power, and most of all, he is their son. As he enters the house with his grandmother, Zeke overhears part of the conversation between his grandfather and his parents. Jaeger asks them if those "social dancing club" meetings they go every night to are really that important to prevent them from spending more time with Zeke, but Dina trusts that one day Zeke will understand what they are actually doing for him.
Jaeger tells Zeke the story of the tragic fall of Lago, a large Marleyan city that was destroyed by Titans 1200 years ago, continuing with the devastation of Monte and the ravaging of Valle; all of which were wiped out by the Eldian Empire over the course of a single day, resulting in hundreds of thousands of Marleyans killed.
Zeke interrupts the story in annoyance, and his grandfather wonders whether Grisha has been really teaching him Eldia's true history. Zeke replies that Grisha has been telling him the same things he learns at school. Jaeger asks him if he wants to become a Warrior and fight for Marley, and Zeke concurs without conviction. He is taken to his bed by his grandfather, but before leaving, he stares at a picture of his deceased aunt Fay.
A few days pass and after getting his training done early, Zeke notices a father and son playing in the street while walking home. Hoping to do the same with Grisha, Zeke goes to see his father, who instead has him study more about their history.
After he gets belittled by both Magath and several other candidates, Zeke leaves the training area in low spirits. He spots a baseball rolling towards him and Xaver calling him to pitch it back. Xaver notices how talented Zeke is in throwing and offers to play catch with him, introducing himself as a Titan researcher as well as the holder of the Beast Titan. Zeke smiles for the first time that day after Xaver continues to remark on his pitching and plays catch with Xaver for the rest of the day.
That night, Zeke overhears part of a plan made by both Grisha and Grice and is transcribed to become part of it to try to become a holder of one of Marley's Titans. He goes back to the training area, but still falls behind the others: Zeke notices his parents there observing but starts to cry as they leave after seeing him struggle to keep up; unknown to Zeke, Xaver notices this as well.
Zeke overhears his parents arguing about his performance and later tells Xaver about this. Xaver mentions that Zeke did not seem to truly want to be a Warrior and mentions how pointless it would be for him to become one due to the numerous drawbacks; he goes on to say that he became one just so he could understand the mysteries behind the Nine Titans and that as honest people, they are not fit to be fighters.
After overhearing the Marleyan authorities are close to discovering the Eldian Restorationists and a harsh reaction from Grisha, Zeke becomes conflicted and goes to Xaver for advice. Xaver then decides the best thing for Zeke is to go to the authorities and report his parents, citing their poor treatment of Zeke for all these years. After Zeke eventually does so, he is accepted by his peers.
As time passes, Xaver's health begins to fade, and he revealed to Zeke that he had discovered through his research that the Founding Titan, in addition to memory alteration, is capable of changing the very body composition of Subjects of Ymir as well. Zeke suggests that if that is true, the Founder could be used to sterilize all Subjects of Ymir and eradicate the Subjects of Ymir in about a hundred years; after a brief pause, Xaver then told Zeke about his own son's death. Xaver had a Marleyan wife who, upon discovering his Eldian heritage promptly killed both their son and herself in shame.
Xaver goes on to say that he tried running away from his sins by using the power of the Titans and tearfully wondered how much better it would have been if he was never born into this world. Zeke promised Xaver that he would inherit his Beast Titan and use it to take the Founder away from both Eldia and Marley, so he can free the people of the world from the terror of the Titans.
Later on, Xaver reveals how to get around Karl Fritz's vow of renouncing war. If a Titan of royal blood comes into contact with the individual who possesses the Founding Titan, they will be able to draw out its power. However, Zeke would not be able to use the power himself. The decision would remain with the individual who possesses the Founder. Xaver tells Zeke to think of himself as a key and to find an individual he would trust with the Founding Titan.
Some time afterward, Zeke ate Xaver and became the new inheritor of the Beast Titan. He put on Xaver's glasses and called him "Father," promising to find a suitable person for their plan.
Zeke learned from Reiner Braun and Bertholdt Hoover that Eren Jaeger possessed the Founding Titan and that Eren's father, a doctor, was missing. Zeke realized that Grisha had not died when he was sent to Paradis Island, and that his father had done the same thing to Eren that he had done to Zeke, and so Zeke promised Eren that he would rescue him.
Years later, Zeke met up with his half-brother, Eren in Marley while he was pretending to be an injured soldier. Eren told Zeke about how he obtained his father's memories and how Grisha had killed the Reiss family to ensure he could take away the Founding Titan. Eren understood that if any of the Reiss children remained alive, he could have been fed to them so they could regain the Founder, and that they were able to live because those children died.
However, Eren told Zeke that he disagreed with Grisha's plan and that if the Eldians had never been born, none of them would have had to suffer. Eren agreed to cooperate with Zeke's euthanization plan.
Back in the cart, Zeke finishes recalling his memories of Xaver; Levi Ackermann overhears part of his muttering and brushes it aside as delusions. He muses that Zeke being eaten by a Titan seems to be a merciful fate for him after killing so many of his comrades, but Zeke says that he saved the lives of the children they would birth from this cruel world.
As Levi stops the wagon and goes to continue cutting off Zeke's growing legs, Zeke suddenly screams out Xaver's name: then, without warning, he jerks his head back and activates the triggering mechanism of the Thunder Spear lodged in his abdomen. Levi is blown into the air as Zeke's body is split in two by the resulting explosion.
Currently Publicly Available Information
Research concerning the unique power of Subjects of Ymir to become Titans. A field of study since the era of the Eldian Empire, it encompasses not only the biology of Titans themselves, but also the ideologies of Eldians who possess the power and how to deal with them. Though researched extensively over many years, the truth of Titans still remains a mystery.