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Floch Forster is a supporting character during the Return to Shiganshina arc and a villain in the later chapters of Attack on Titan.
Initially a member of the Survey Corps and one of the nine survivors of the Battle of Shiganshina, Floch eventually dived into extremistic views after the existence of Marley is revealed to the population of Paradis Island. Believing that only Eren Yeager can lead Eldia to victory against Marley, Floch either forms or joins the extremistic Yeagerist Faction which plans to make Eren Yeager the leader of Eldia - by any means neccessary.
In the anime, he is voiced by Kenshō Ono (Japanese) and Matt Shipman (English).
Floch joined the military inside the walls during the year 847 and was part of the 104th training corps. After graduating, he joined the Garrison where he served for several years. However, after the uprising within the walls, several members of the Garrison - including Floch - joined the Survey Corps. When the Survey Corps prepared their journey to Shiganshina in order to retake Wall Maria, Floch introduced himself to the "veterans" of the Survey Corps, who joined the military during the 104th training corps as well. Given that they had fought several battles with Titans in the meanwhile and had suffered many losses, Floch was shocked to see how much these people had changed.
Battle of Shiganshina
When the Survey Corps reaches Shiganshina, Floch and other new recruits are put in charge of taking care of the horses, causing them to remain in the destroyed village outside of Shiganshina on the inside of Wall Maria. However, suddenly the Beast Titan appears with several smaller pure Titans, cutting off the way back to Wall Rose. While most of the Survey Corps is dealing with the Armored Titan and the Colossus Titan inside Shiganshina, the Beast Titan starts hurling stones and boulders at Levis Team, wiping them out and causing Levi to retreat back to Floch and the others, who are panicking. In his fear, Floch lets go of the horses, having realizes that they are trapped and that there is no way of escaping and that they will all die a pointless death.
Eventually, Commander Erwin and Levi come up with a plan to kill the Beast Titan - while Erwin and the rest of the new recruits will ride a suicide attack by riding at the Beast Titan frontally, Levi will sneak up to him from the side and use the Titan's focus on Erwin's group to deal the killing blow. Floch is horrified to hear this and asks if Erwin expects them to fight if they are all going to die anyways. Erwin confirms this and tells them, that it is their duty to fight for humanity and to give meaning to the deaths of all other soldiers, who came before them. Accordingly, the suicide charge is formed and Erwin leads his recruits into battle by frontally storming at the Beast Titan, who kills most of them with the first barrage of projectile he is throwing at them. While Erwin is the first to fall, all other recruits are killed by the Beast Titan's projectiles as well.
After Levi has attacked the Beast Titan and has defeated him successfully, Floch rises from the field, being the only survivor of the suicide charge. Horrified, he walks through the bodies of his fallen comrades and desperately searches for other survivors, eventually finding the mortally wounded but still breathing Erwin. He grabs the commander and carries him back to the Wall, where he finds Levi, Eren and Mikasa standing over the mortally wounded Armin, who has been hurt during the fight against the Colossus Titan. Levi is about to inject Armin with the titam serum so that he can eat Bertolt and become a Titan Shifter, but Floch informs Levi that Erwin has survived and should be the one to receive the saving injection. As Eren and Mikasa are unwilling to let their friend Armin die, an argument erupts during which Floch claims that only a man like Erwin can lead humanity to victory against the titans. As Levi is about to make his choice, Floch forcibly restrains Eren and moves him to another rooftop while Hanji takes Mikasa.
From the rooftop, the group watches as Levi injects Armin with the infusion, choosing his life over Erwin's. After the group has gone to the Yeager basement and has found the truth about the world, the sole nine survivors of the Survey Corps return to Shiganshina, where there is to be a ceremony in their honor. Moments before the ceremony starts, Floch bitterly reveals to Hitch Dreyse that in his final moments, Marlowe remained brave and calm but that he must have regretted his final actions anyway. When the angry Jean demands to know why Floch would say that, Floch responds that someone must speak the truth about what happened. He also angrily states that every sane person would have chosen Erwin over Armin; stating that Eren, Mikasa and Levi let their personal feelings overwhelm them and that saving Erwin would have been the rational choice. He commends Mikasa for surendering to the logical choice in the end while calling Eren childish and irrational.
In the following years, Paradis - now the nation of Eldia - takes several prisoners by capturing a ship from Marley's expedition fleet. Floch is tasked with guarding Yelena, who somehow convinces him to arrange a meeting with Eren Yeager and herself. During the meeting, Yelena reveals some groundbreaking information to Eren, causing a radical personality change in him. Eren allies himself with his half-brother Zeke and Floch and other members of the military join his side - forming the splinter group known as Yeagerists. Their plan is to make Eren the leader of Eldia because they think that his titan power is the only way of destroying Marley. Ten months later, Eren initiates an attack on the Liberio Internment Zone in Marley and when the Survey Corps comes to save them, Floch uses explosives initially intended for abandoned buildings to destroy buildings full of civillians as payback for the countless deaths Marley's titans caused to Paradis. When he is confronted by Jean for this action, he is unrepentant and instead claims that Eren is the only one who understands that they have to fight their enemies.
After the attack is over and the Survey Corps flees in their blimp, Floch and other Yeagerists celebrate the first victory of the "New Eldian Empire". In their celebration, they do not realize that two child soldiers of the Marley Warrior Program, Gabi and Falco, have entered the blimp. Gabi is able to shoot Sasha Blouse and kills her, before Floch and his comrades swarm the children and grab them. Floch plans to throw them out of the blimp mid-air, but Jean forbids it, claiming that it would have no purpose to kill the children. After the blimp returns to Paradis, Eren is imprisoned for his attack on Liberio. This causes Floch and other Yeagerists in the military, Wim and Louise, to leak the news about Eren's imprisonment to the public, causing massive protests. After Hanji realizes what Floch and the others have done, she demands an explanation but Floch calmly claims that Eren has nothing wrong and that his actions saved the people of Paradis. He claims that Paradis is safe as long as the Founding Titan remains with Eren. Hanji then orders Floch, Wim and Louise to be arrested.
Nonetheless, loyalists in the military free Floch and other Yeagerists from prison and Eren can escape as well. The group meets up outside the city and Floch reveals to Eren, that they took precautions to prevent the military from feeding Eren to a more loyal titan - they assassinated Premier Darius Zackly, who seemed to have harbored this intention for some time. After the bomb attack on Zackly, the group heads to a restaurant where they forcefully apprehend Hanji, Armin, Mikasa, Jean, Connie, the Blouse Family as well as Gabi and Falco. Floch takes them all prisoner and when Hanji wants him that they discovered that Zeke Yeager might have spiked the wine of Paradis with his own spinal fluid - giving him the power to turn everyone who drank it; mostly high-ranking military personel; into Titans - Floch implies that he knew about this all along and that it is actually part of the Yeagerists plans. He smugly tells Hanji to be quiet and then has all of them arrested and taken to Shiganshina.
In Shiganshina, Floch has most of his prisoners put in a cell. However, he takes Hanji along when he and his followers storm the training grounds where Keith Shadis is currently training the 109th Training Corps. Floch shouts that the unit is now under his command and holds a passionate speech in which he tells the trainees that they have to take their future into their own hands and that they need to fight for the survival of Eldia rather than clinging to the past and old traditions, like Shadis does. When the trainees agree to join him, Floch demands that they brutally beat up Shadis until he can no longer stand. After the violent initiation is done, Floch admits all of them to the Yeagerist faction before ordering Hanji to take him to the place where Zeke Yeager is currently being held prisoner.