The Reiss family was the descendants of Karl Fritz, the first king of walls. They lived a quiet and luxurious life away from political conflicts after the conclusion of the Great Titan War. In order to ensure that they do not draw too much attention towards them, they set up a false King while keeping the reality of the outside world and the Titans a secret. After every 13 years, the Founding Titan was passed down between the ruling monarchs, and Eldians remained largely ignorant. While things always worked out for them when Grisha Yaeger confronted the family for their inaction and indifference, things ended tragically for the royals.
Why Did Grisha Yaeger Kill the Reiss Family?
As the inheritors of the Founding Titan, the Reiss family have played an active role in upholding King Fritz’s vow to renounce war. Although there have been members of the family who have disagreed with his ideology, as soon as someone like that inherited the powers, they mellowed down and completely forgot about their revolting ideas. It happens because the ideology of the royals who inherit the Founding Titan is tainted by the pacifist principles of the first king of the walls.
So, even if a member of the Reiss family acquires the powers of the Founding Titan with the hope to fix the world according to their principles, they would fail irrespective of the strength of their resolve. In season 3, we see Uri Reiss experience the ideological weight of the first king of the walls and completely forget about her disagreements after becoming the new holder of the Founding Titan. Frieda Reiss experiences something similar, and it appears that the crimes of the past seem too great for the royal inheritors, which is why they preach about atonement.
When Grisha Yaeger confronts the Reiss family, he pleads in front of them to save Eldians from the approaching Titans who are about to break wall Maria. But how does Eren’s father know that Reiner and Bertolt are going to attack? Every Titan has a unique characteristic of its own, and Grisha’s Titan is no different. The holder of the Attack Titan can see the memories of its future inheritors. So, even before the fall of Wall Maria, Grisha knows the tragedy that is about to unfold.
Furthermore, he has always been a staunch supporter of the restoration of Eldia to protect his people, who have been oppressed for centuries following the conclusion of the Great Titan War. Therefore, he pleads with Frieda to do something before the walls are broken, and hundreds of Titans are unleashed on innocent people. Unfortunately, irrespective of what she may have made of the situation if she was not the holder of the Founding Titan, Frieda is under the influence of King Fritz’s vow to renounce war. So, instead of doing something to help the people that she rules behind closed doors, she argues that it’s time for the people to atone for the crimes that were committed thousands of years ago.
Grisha is appalled by the disregard for innocent people’s life and realizes that there is only one way to stop the eventual ethnic cleansing of the Eldians. He must acquire the Founding Titan and ensure that the royal bloodline is dealt with once and for all so that the effects of King Fritz’s vow are limited, at least on Paradis Island. Even though he knows that a non-royal cannot fully use the powers of the Founding Titan, Grisha realizes that it could be extremely beneficial, at least in defending his people from the horrors that are about to unfold.
Even though he hesitates in putting his plans to action and feels that he can not murder people, it is eventually Eren and his memories that reassure him that it is the only way for the eventual restoration of Eldia. Eren reminds his father of the sacrifices of the fellow restorationists and his duty to save his people, following which Grisha murders every single member of the Reiss family and acquires the Founding Titan.
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