|And just like that, everything changed. At that terrible moment, in our hearts, we knew. Home was a pen. Humanity, cattle.|
|— Humanity's desperate battle begins|
The Fall of Wall Maria (ウォール・マリア陥落 Wōru Maria kanraku?) was a tragic disaster which began when Shiganshina Distict came under the attack of the Colossal Titan, Armored Titan, and Female Titan, in which humanity was forced to retreat to Wall Rose as the Titans entered humanity's territory for the first time in a hundred years.
Over two decades ago, the nation of Marley began to consider the necessity of claiming the immense amount of fossil fuels on Paradis Island where the majority of the remnants of the nation of Eldia lived within the three Walls: Maria, Rose, and Sina.
Over eighty years ago, King Karl Fritz had issued an ultimatum to the nation of Marley at the end of the Great Titan War: if Marley made any move of hostility against the Eldians of Paradis Island, the King would use the Founding Titan to release the countless Colossal Titans contained within the Walls. In order to claim Paradis Island without a direct act of war, the Marleyans chose to begin a Warrior program. In this program, low-class Eldian citizens within Marley would offer their children between the ages of 5 and 7 to the Marleyan military, where they would train until the top cadets would be chosen to inherit the seven Titans in Marleyan control, obtained during the Great Titan War.
Over a decade later, six of the seven Marley's Titans were inherited by their top Warriors: the Beast Titan to Zeke Jaeger, the Armored Titan to Reiner Braun, the Colossal Titan to Bertholdt Hoover, the Female Titan to Annie Leonhart, the Jaw Titan to Marcel Galliard, and the Cart Titan to Pieck. Out of these six Warriors, four were chosen to be sent out from Marley to begin the attack on Paradis Island: Bertholdt, Reiner, Annie, and Marcel. Zeke and Pieck would remain behind in Marley to defend against local conflicts and other nations. The seventh Titan, the War Hammer Titan, would be placed under the possession by the Tybur family.
The four Warriors travel from the borderline of Paradis Island to the Walls, Reiner was nearly eaten by a Titan. Marcel sacrificed himself to save Reiner, who watched helplessly as their friend was consumed. As they continued on their mission, the Titan absorbed the power of the Jaw Titan and returned to its human form as Ymir, an Eldian girl who had been turned into a Titan around sixty years before. With her humanity regained, Ymir made her way to the Walls to live a new life.
Tensions arose between the Warriors following Marcel's death, and some considered returning the borderline in defeat. However, after some conflict, it was decided that they would continue their mission to retrieve the Founder lest their failure cost them their right to live upon their return to Marley. The three travel to Wall Maria's outer district, Shiganshina, where Bertholdt transforms and destroys the gate.
Meanwhile on Paradis, on the morning before the fall, Commander Keith Sadies returned to Shiganshina District from an expedition beyond Wall Maria with devastating losses. With the Scout Regiment's drastically reduced numbers, the people of the Walls were all the more susceptible to the Titans.
Elsewhere in Shiganshina, Grisha Jaeger made plans to travel to the interior on an appointment. Before leaving his home, he promised his son Eren Jaeger that upon his return, he would show him the secret he had kept secret in the basement of their home.
In the afternoon following the return of the defeated Scout Regiment, the attack on the Walls began when the Warriors arrived at Wall Maria. As the Colossal Titan, Bertholdt appeared beyond the south gate of Shiganshina District, breaking the gate apart and breaching Wall Maria in a single kick. Presumably at this time, Annie Leonhart used the Female Titan to attract countless Titans to the breach where they would invade humanity's territory. As Titans began to enter the district, the civilians started to evacuate in a horrified panic while the Garrison set up a hasty defense.
During the massacre, Eren Jaeger and Mikasa Ackermann rushed back to their home to find that their mother Carla was trapped in the debris and unable to move, and the two children desperately tried to free her without success. Carla pleaded them to save themselves when the Garrison soldier Hannes, a family friend, rushed to their aid. Confident he could slay an incoming Titan, Hannes rushed into action hoping to save the entire family, but soon found himself unable to face the Titan. Unnerved and losing the will to fight, Hannes saved Eren and Mikasa and evacuated with them as Carla, accepting her fate, was eaten by the Titan as Eren watched.
Unable to contain the invading Titans, the Garrison evacuated any survivors they could to the gate and packed them into ferries that would transport them to Wall Rose. A small group of soldiers under the command of Hugo assigned cannons to defend the gate, trying to hold off the advancing Titans. Hannes argued against closing the gate, which would stop the advance of the Titans but also doom the civilians who had not yet evacuated. Before a conclusion could be made, the Armored Titan charged the north gate of Shiganshina, with Garrison cannonfire proving useless against him. The Armored Titan succeeded in breaching the north gate, and with that Wall Maria was fallen.
The Reiss family massacre
In the interior, Grisha Jaeger arrived at the Reiss Chapel where the family had gathered in response to the crisis. Grisha approached Frieda Reiss, queen of the Walls, and begged for her to use the power of the Founding Titan to defeat the Titan threat and save her people. Being overcome by the will of Karl Fritz, Frieda refused Grisha's pleas. Grisha understood that Frieda would be unable to act due to the First Reiss King's will, and he decided to take the power of the Founder for himself. Grisha transformed into the Attack Titan and battled Frieda's Founding Titan, quickly defeating her. He ate Frieda out of her Titan's nape, stealing the Founding Titan, and afterward slaughtered the members of the Reiss family within the underground of the chapel, with only the father Rod Reiss managing to escape from the slaughter.
Afterwards, Grisha made his way south to where the refugees from Shiganshina District would arrive. When the refugees from Wall Maria entered the safety of Wall Rose, Grisha had arrived at the scene to search for his family. He reunited with Mikasa and Eren, the latter of which told him of his mother's death. Ex-commander Keith Sadies who was nearby was distraught at the news, and Grisha led his son into a nearby forest, urging Keith to stay uninvolved.
Within the forest, Grisha urged Eren to return to Shiganshina in the future in order to discover the secrets within the basement of their home. He injected Eren with a Titan serum stolen from the Reiss family, turning his son into a Titan. Eren's Titan consumed Grisha, inheriting his Titan power and the unusable Founding Titan with it. Eren fell into a state of shock, falling unconscious and forgetting the event, and Keith Sadies found him shortly afterward and returned him to the refugee center.
With an abundance of refugees coming into Wall Rose's territory, humanity faced a severe food crisis. Refugees were tasked with working the farmlands of Wall Rose to alleviate the impending shortages. In order to alleviate the food shortages, the royal government made plans to announce an operation to reclaim Wall Maria. While the operation's public purpose would be to reclaim humanity's lost territory, its true purpose would be to thin the human population so that the surviving residents of Walls Rose and Sina would not be at a loss for necessary food and supplies.
The three surviving Warriors responsible for the fall of Wall Maria, Bertholdt, Reiner, and Annie, took advantage of the chaos and posed as ordinary refugees to infiltrate Wall Rose. In two years, they would enlist in the 104th Cadet Corps in order to earn placement in the top ten of their corps, gaining privileges to join the Military Police Regiment along with easy access to the interior where the royal family resided.