Liberio (レベリオ Reberio?, also translated as Rebellio) is a Marleyan city that contains an internment zone (収容区 Shūyō-ku?), a designated area of land for Eldians on the mainland to live in. It is the hometown (故郷 Kokyō?) of many of the Warriors as well as Grisha Yeager.
Liberio is a metropolis intersected by a large river near a railway. It has at least three notable sections: the Marleyan area, where the ethnic Marleyan people reside and where the Warrior Headquarters is located; the internment zone, where residents with Eldian blood live; and an industrial zone.
At the end of the Great Titan War, King Karl Fritz and many Eldians settled on Paradis Island, fleeing from the mainland war. However, some Eldians stayed behind on the continent were overtaken by Marley, the enemy nation.
Rather than slaughtering the remaining Eldians on the continental mainland, the nation of Marley chose to isolate the Eldians into designated internment zones. While Marley claimed to be extending mercy towards the devil's descendants, the internment zones were in reality created to store Eldians until the Founding Titan could be acquired from the King of the Walls on Paradis Island in the future. Around this time, a statue of the Marleyan hero Helos is commissioned and built.
One of the internment zones established on the mainland was within the city of Liberio. In Grisha Yeager's childhood, he and his family lived a quiet life in Liberio until Grisha decided to wander beyond the internment zone walls with his sister Faye without authorization. They were found by Public Security Authority officers Kruger and Gross, the former punishing Grisha while the latter claimed to escort Faye back to Liberio. In reality, Gross had taken Faye to his home and fed her to his sons' dogs, leaving her corpse by the river near Liberio. This event shattered Grisha's respect for his unresponsive father and kindled a self-hatred over his foolish decision.
After some years had passed, Grisha joined the Eldian Restorationists, a secret rebellious group in Liberio who, while cooperating with the Eldian spy under the alias "the Owl," sought to restore Eldia's former glory. There he met Dina Fritz, the last living descendant of the royal family which remained behind on the mainland after the war. Grisha married Dina a year after joining the Restorationists, and together they became the parents of a child named Zeke, whose royal blood Grisha planned to exploit for Eldia's favor in the future.
Years later, the Marley government announced to the people of Liberio that a Warrior program would accept Eldian children between the ages of five to seven to inherit the powers of the seven Titans that Marley had taken during the war. Seeing an opportunity, Grisha sent his son Zeke into the Warriors to act as a double agent for Eldia. However, when Zeke turned seven, he betrayed the Eldian Restorationists to the Public Security Authorities, who arrested them all and sent them away to Paradis Island to become Pure Titans.
Before the Paradis Island Operation, Reiner Braun, Bertolt Hoover, Annie Leonhart, and her father lived their days in Liberio, a place which Reiner and Bertolt would later refer to only as their "hometown." Before Annie's departure from Liberio, her father ensured her that he would support her even if all the world hated her, and that he would only ask that she would return home.
During their days spent in the 104th Training Corps, Reiner and Bertolt claimed that their hometown was within the southeastern mountainous region of Wall Maria and that their town had been overrun by Titans without warning during the fall of Wall Maria. Reiner in particular expressed a strong desire to return to his hometown in the future.
During the Wall Rose invasion when the Survey Corps recruits battle the Titans at Utgard Castle, Reiner comes close to death by a Titan and fears for the end of his life before he is saved by Bertolt. At this time he strengthens his will, filled with determination to return to his hometown. He shares his resolve with Bertolt, who understands the true meaning of what Reiner says and agrees with his hopeful words.
The next morning, Reiner begins to lose hope for his situation due to the injury inflicted on his arm at Utgard; Bertolt encourages him by reminding him of their imminent return to their hometown. Not long afterward, the two reveal their Titan identities as the Armored and Colossus Titans and attempt to capture Eren Yeager, whom they must bring to their hometown as part of the plan to regain the Founder. They succeed in capturing him and escape to a Titan Forest.
While in the Titan forest, Reiner reminds Bertolt that their most favorable course of action is to return Annie Leonhart, Historia Reiss, and the "Coordinate" to their hometown in order for their mission to be complete. Reiner also suggests that Bertolt should confess his true feelings to Annie upon their return, but Bertolt denies any such affections. Later, when Reiner and Bertolt attempt to escape with their captives Eren and Ymir, they inform the others that Eren's life is not up for negotiation and that he is going to be taken to their hometown. Armin taunted Bertolt at the thought of leaving Annie behind, causing him to attempt an attack and exposing a vulnerable moment for Erwin Smith to free Eren.
Ymir and the fleeing Warriors arrive in the ruins of Shiganshina District later that night, where Reiner lets Ymir know that her rescue is hopeless if they take her to their hometown. Ymir accepts her fate, believing that she owes Reiner and Bertolt a favor for indirectly freeing her from her life as a Titan five years before.
In the aftermath of the battle of Shiganshina District, the surviving members of the Survey Corps learn of the existence of Liberio and the rest of the outside world through Grisha Yeager's autobiographical writings, kept hidden in the basement of his former home.
Four years later, the nation of Marley is victorious against the Mid-East Allied Forces, and the Warrior candidates as well as the rest of the Eldian forces return to Liberio by train and reunite with their families.
The injured Eldian soldiers are also taken to the internment zone's hospital. One of the current Warrior candidates, Falco Grice, meets a man named Kruger and grows to respect the soldier. He delivers numerous letters for Kruger to an unregulated postbox outside Liberio.
The Tybur family visits Liberio so Willy Tybur, the head of the family, can see the statue of Helos at the military's headquarters. He also meets with Commander Theo Magath and takes him into his confidence. One month later, Willy invites representatives from the world's nations to a festival in Liberio's internment zone.
The festival is held, with numerous people setting up stalls in order to impress foreign visitors. The people of the internment zone also partake in the celebration over the course of the day. At night, crowds of civilians, army officials, and foreign ambassadors gather to hear Willy's speech. Before the curtain rises, Falco Grice asks for a moment of Reiner's time, and leads him to a basement where "Mister Kruger," now identifiable as Eren Yeager, awaits.
The curtain rises and Willy takes the stage, beginning his speech with a production recounting the history of the world, and the horrors of the Titans. In an interlude, the Warriors Pieck and Porco Galliard are summoned by a supposed Marleyan soldier, who later traps them in a confinement area.
Willy concludes his speech and as he gives a declaration of war, Eren transforms into the Attack Titan, emerging from the building behind Willy and crushing the stage. This attack sends debris flying into the crowd and kills Willy.
The Attack Titan begins a rampage, slaughtering key military personnel with little regard for collateral damage. The massacre sends pandemonium into the crowd, creating a human stampede as people rush to escape the area surrounding the stands.
Having survived the collapsed stage, the Younger sister of Willy praises her brother's legacy and transforms into the War Hammer Titan to battle the Attack Titan. Meanwhile, Pieck and Galliard escape their confinement area with help from the Cart Titan's Panzer Unit. 
The Survey Corps begins their attack in earnest, shooting down the Marleyan infantry, as well as any armed Public Security Authorities in the area. A group of soldiers led by Floch Forster set fire to residential buildings. The Corps blocks off roads and installs lights on top of buildings to direct their escape airship later.
The ensuing conflict wrecks havoc in the vicinity, with the Warriors generally controlling the flow of battle. Inside the relative safety of a building, Magath calls in thirty thousand soldiers stationed nearby. He instructs them to seal off the internment zone to prevent the escape of the enemy soldiers.
In the nearby harbor, the navy forces summoned to Liberio prepare to dock their battleships. The transformation of Armin Arlert into the Colossus Titan prevents this, destroying the harbor and ships and sending a shock-wave into the internment zone. The battle continues with a reversal of dominance by the Survey Corps when they incapacitate most of the Warriors and even appear to kill Zeke Yeager's Beast Titan. The Corps successfully retreats on the airship following the lights previously set by Jean Kirstein's squad.
The next day, the Marleyan military is seen excavating the site of victims, which includes children. The hardened remains of the War Hammer Titan looms over the carnage. At the site of Zeke's "death," they can only find his limbs, suggesting that he faked his demise.