Karl Fritz, the first king of walls, was descended from the Reiss family. After the Great Titan War, they enjoyed a tranquil and affluent existence away from political strife. To avoid drawing too much attention to themselves, they put up a counterfeit King while keeping the reality of the outside world and the Titans hidden. The Founding Titan was passed down between the ruling kings every 13 years, and Eldians were generally unaware. When Grisha Yaeger challenged the royal family about their inaction and apathy, things always worked out for them, but things ended horribly for the royals.

Grisha Yaeger’s motive for murdering the Reiss family is unknown.

The Reiss family, as the heirs of the Founding Titan, have played an active part in honoring King Fritz’s commitment to abstain from violence. Although some members of the family disagreed with his beliefs, as soon as someone like that gained the authority, they calmed down and forgot about their disgusting ideas. It occurs because the pacifist ideas of the first king of the walls poison the mindset of the royals who inherit the Founding Titan.

So, even if a member of the Reiss family gets the powers of the Founding Titan in the aim of repairing the world in accordance with their values, they will fail regardless of how strong their resolve is. In Season 3, Uri Reiss feels the ideological weight of the first king of the walls and forgets about her disputes after becoming the new holder of the Founding Titan. Frieda Reiss had a similar experience, and it appears that the royal inheritors’ previous misdeeds are too enormous for them, which is why they preach about atonement.

When Grisha Yaeger confronts the Reiss family, he begs them to save the Eldians from the impending Titans who are about to breach the wall Maria. But how does Eren’s father know Reiner and Bertolt are planning a surprise attack? Every Titan has a distinct personality, and Grisha’s Titan is no exception. The Attack Titan’s possessor may glimpse the memories of its future inheritors. So, even before the fall of Wall Maria, Grisha is aware of the impending calamity.

Furthermore, he has always been a staunch advocate of Eldia’s restoration in order to defend his people, who have been subjugated for generations since the end of the Great Titan War. As a result, he begs Frieda to intervene before the walls are breached and hundreds of Titans are unleashed on innocent people. Frieda, despite what she might have thought of the situation if she hadn’t been the keeper of the Founding Titan, is swayed by King Fritz’s resolve to abstain from war. So, rather than doing anything to help the people over whom she rules behind closed doors, she claims that it is time for the people to atone for crimes committed thousands of years ago.

Grisha is shocked by the disregard for innocent people’s lives and knows that there is only one way to save the Eldians from being ethnically cleansed. He must obtain the Founding Titan and ensure that the royal lineage is dealt with once and for all in order to restrict the ramifications of King Fritz’s pledge, at least on Paradis Island. Even while he is aware that a non-royal cannot fully utilize the powers of the Founding Titan, Grisha recognizes that they could be highly useful, at least in shielding his people from the horrors that are about to unfold.

Even though he is hesitant to carry out his intentions because he believes he cannot murder people, Eren and his memories eventually convince him that it is the only way to restore Eldia. Grisha murders every member of the Reiss family and acquires the Founding Titan after Eren reminds his father of the sacrifices of his fellow restorationists and his obligation to save his people.