Eren didn't turn “evil” per se so much as he saw that the world did not have any kind of clemency toward his race. It's because he saw that the entire world hated him and his kind that the only solution he could arrive at was to kill the entire world.
12 Eren Has Always Been Reckless & Violent
Eren's reckless personality and tendency to disregard everyone around him was a red flag from the jump. He didn't see the issue with Erwin's plan for him to fight the Female Titan in Stohess District, despite the obvious amounts of collateral damage that would result.
It was because of his future-seeing abilities that most of the story transpired the way it did, which makes Eren seem even eviler than how he was initially presented. Eren wasn't always an evil character, but there are plenty of hints sprinkled throughout the series regarding what he was destined to become.
To some extent, yes. Eren did encourage Grisha to kill the members of the royal family and sent future memories so that he would know that there would be no future for humanity inside the walls if the founding titan remained with them because of the curse.
Eren did plan a lot. He still got surprised sometimes, so I don't think he planned everything. However, he planned enough. We know he orchestrated the massacre of the Reiss family.
Eren's goal is to eliminate the entire world except for Paradis, but keeping his fellow Paradisans alive is also extremely important to him, especially his close friends.
Eren Yeager - Eren was Carla's only son, who she considered to be cute since he was a baby. She felt a deep love for him, seen when she told him not to join the Survey Corps because it is too dangerous.
Eren's intended genocide of the human race undeniably makes him an irredeemable character -- but the Rumbling isn't the only one of Eren's sins that is wholly unforgivable. Eren has brought unimaginable suffering upon his closest friends by forcing them to kill their own comrades just to stop him.
Eren was never brainwashed. Zeke overlooks the past and realizes Eren always had darkness in him. Eren was surrounded by love and affection from his friends and family, including their father.
Like Dent, he wants to take the Machiavellian measures to do what's right, even if it's at the expense of his own humanity. Ultimately, however, both their actions lead to tragedy and Eren inevitably becomes the villain of his own series.
Eren was devastated by Sasha's passing. However, because of what he experienced and what he had to do to save the Eldians, hearing Sasha's final words made sense to him and brought back memories of when they were younger, and it was easier to hate the Titans for the devastation they had caused.
Why didn't Zeke tried to eat Eren and take the founding titan as he already have royal blood? Why didn't he took founding titan from Eren? He already has royal blood. From this he can use the power of Founding titan to it's full extent and achieve his goal.
Eren hates Mikasa's supposed lack of free will and claims he always hated her for having no freedom. Eren points to Mikasa's headaches as proof her Ackerman bloodline is all that's keeping them together.
It was then that Eren realized the hatred for Eldians (especially on Paradis) would never end, and it would be better to just destroy the world leaving only Eldians from the island “that bore and raised him”.
Because Eren wanted to end the titans which requires his friends to kill him but if they does that they can't go back to Paradis. So they needs a place. Also without any enemy paradis will get into civil war like they did before.
In AOT chapter 139, Eren reveals that he turned the bad guy so that he could make Armin and the alliance the heroes who saved humanity from extinction by stopping him. In short, he wanted to die at the hands of his friends in order to guarantee their freedom. He sacrificed his life and freedom for theirs.
Eren's Ultimate Fate in Attack on Titan
After making it inside Eren's Titan mouth thanks to assistance from Levi, Mikasa decapitated Eren's human body and kissed him goodbye for the first and last time. The final chapter confirms Eren's death -- for good this time.
Recognizing the fire in Eren's eyes, and afraid that he will get himself killed if he joins the Survey Corps, Keith decides to sabotage Eren's entry into the military.
The idea of "the future doesn't change" in AoT is that even if Eren tries to change the outcome of him saving Ramzi, he can't make himself because that's just the person he is. Eren Jaeger will save Ramzi, that future doesn't change because who Eren is as a person doesn't change.
Eren Yeager was the main protagonist of the Attack On Titan series and the wielder of the Attack, Founding, and War Hammer Titans. In spite of his moral decline ever since the revelations about Marley, there have been many instances where he proved himself to be a good person.
Eren didn't have a choice because he was always a slave to his own ideal of absolute freedom (freedom without external restraints).
When Season-3-Eren kissed Historia's hand, he saw Grisha's memory of his slaughter of the Reiss family, which Grisha did on Future Eren's orders, with Season-4-Eren present via Zeke's Founding Titan powers.
Activating the Coordinate ability, a power that he did not know that he had, Eren seemingly started to gain control over the surrounding Titans and they proceeded to kill the Smiling Titan.
Love Confession — Eren confesses to Armin that he always loved Mikasa, and can't bare seeing her love another man. Alternate Universe — Eren sends Mikasa a vision where Mikasa truly were to confess her feelings to Eren, the two then run away to live together as a couple for the remaining of Eren's final years.
His Mom Was Eaten By A Titan
Eren's seemingly peaceful life is met with chaos almost immediately when the Titans get through the wall and his mom, Carla, is crushed in rubble and he cannot pull her out. His mom then gets eaten by a Titan right in front of him shortly after he has to run to avoid getting eaten as well.