After uncovering the secrets of the basement in Shiganshina District, Eren and the survey corps found out Zeke’s true identity. The boy-wonder Zeke Yeager none other Grisha and Dina Fritz’s son, which made him Eren’s half brother. While he seems to have some sort of a soft spot for Eren, Zeke is someone who betrayed his parents to the Marley officials. What could be the reason for this?

Let’s get this piece of opinion out in the open first, Grisha was not a good father. He was a fanatic who cared more about his race. So, while we blame Zeke for betraying, we should also blame Grisha for putting Zeke in such a position. But first, lets try to understand what was Zeke’s state of mind, which pushed him into taking such a drastic step.

After finding out what they believed was the true history of the Eldians, Grisha Yeager and the Eldian Restorationists started to look for every means possible to take over Marley. After marrying Dina Fritz, a royal blood woman, sent by the Owl, Grisha had a child named Zeke.

The following article contains major spoilers for Attack on Titan manga. Read ahead at your own discretion.

Eren always had a purpose to “slaughter every last Titan”. While his circumstances were involved, this was a choice that Eren made freely. On the other hand, Zeke never got to make a choice on his own neither did he have any conviction. The only thing that made him go on as a Warrior was to seek all the love from his parents. 

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From a very young age, Zeke was made to study both the Marleyan and Grisha’s version of the Eldian History and he also understood both of them. Zeke was not fond of war, this made him feel uneasy with what his father taught him. Also, as he lagged behind in training, his parents gave up on him. He expected his parents to protect him, instead he was more and more exposed to the danger without any compassion or appreciation.

Thus when he finally met the former beast titan user, Tom Ksaver, who showed him the affection he craved for, Zeke instantly bonded with him. Tom was everything that Zeke expected his father to be. He even addressed him as “dad” later in the manga.

So when Zeke found out that the Marleyan authorities were closing in on the Eldian restorationists, he went to Tom for advice. And it was Tom who suggested that Zeke save his own life and his grandparents by ratting out Grisha and Dina to gain Marley’s trust. Tom acted like how a parent would, in order to keep his child safe.

Thus, long story short, Zeke betrayed his parents to keep himself and his granparents safe from becoming a mindless Titan. He realised that the Marleyan authorities were closing in on the restorationists. And according to Tom there was no other way to save his grandparents, whom he loved more than his parents.

Zeke’s interaction with Tom would also lead him to formulate his secret plan, which he saw as the only way to save the Eldians and the world. The treatment that Zeke got as a child from the Marleyans triggered his insecurity and made him internalize the racism targeted towards the subjects of Ymir and bound him to betray his parents as an atonement.

Tom and Zeke’s ideology to free the Eldians from anymore suffering by ending their lives and restricting them from further bearing children of “devils” had become their ultimate goal. Even if he hated it and felt sorry for his parents, he made the choice to save the people dear to him and end the suffering of as many Eldians as he can.