|We lured that Female Titan here so we could capture it, I bet. That's the only reason I can think of for why they only told certain soldiers about this operation. But does that mean there are humans in our ranks who are trying to destroy the Walls?|
|— Jean Kirstein realizes the true intent of the mission|
The 57th Expedition Outside the Walls (第57回壁外調査 Dai 57 Kai Hekigai Chōsa?) was a mission undertaken by the Survey Corps to plot a course from Karanes District to Shiganshina District. The expedition was sabotaged by the Female Titan and subsequently considered a failure.
In the days following the battle of Trost District, Eren Yeager's Titan powers had become public knowledge. The interior districts in particular fell into a state of general confusion over the news, highly skeptical of the claims presented by both the Royal Government and the civilian merchants. Those in positions of authority within the government regarded Eren as a threat, though they publicly abided by their policy of non-intervention in matters not concerning Wall Sheena. On the other hand, many saw Eren as a hero for his actions, and tensions rose between the people of Wall Sheena and Wall Rose. At this time, the threat of civil war was being considered by Military Police Brigade Commander Nile Dok.
At this time, Eren's Titan abilities also became known to Rod Reiss, the last known living member of the Reiss family, the true royal family living in secret as nobles in Wall Sheena. Understanding that Eren Yeager must have been the holder of the Founding Titan, the power of the Reiss family stolen five years ago, orders were given to the Military Police that Eren must be taken alive into their custody.
Shortly after Eren awoke from his coma, a military tribunal led by Commander-in-Chief Darius Zackly was held in order to determine the fate of Eren Yeager. Several merchants, representatives of the Church of the Walls, and other political figures were present at this time. Commander Nile Dok of the Military Police spoke his concerns of civil war, claiming that Eren would be examined thoroughly before being disposed of. Commander Erwin Smith of the Survey Corps proposed inducting Eren into the Survey Corps as a full-fledged member with his Titan powers being put to use in reclaiming Wall Maria. Tensions arose in the courtroom, though eventually it was decided that Eren would be handed over to the custody of the Survey Corps under the condition that his powers would be used in the next expedition beyond Wall Rose. If the expedition were to fail, Eren's fate would once again be at the military's discretion.
Preparations for the expedition
After officially joining the Survey Corps, Eren was placed under the command of Captain Levi Ackerman, who had handpicked a selection of elite Survey Corps soldiers known as the Special Operations Squad to guard Eren and kill him if necessary. After cleaning and refurbishing an abandoned Survey Corps fortress, Eren was introduced to Squad Leader Hange Zoë, who would be in charge of performing experimentation on Eren's Titan abilities. Hange informed Eren of the Survey Corps' findings in the investigation of "Sonny" and "Bean," the two Titans that had been captured in the final moments of the battle of Trost.
At this time, Annie Leonhart infiltrated the Survey Corps grounds and killed Sonny and Bean in order to hinder the Survey Corps' research. Members of the 104th Training Corps were soon investigated concerning the matter, and Annie presented Marco Bott's vertical maneuvering equipment in order to pass the examination, though this was noticed by her fellow trainee Armin Arlert. Later that day, Erwin Smith held a speech offering to accept new members into the Survey Corps, making clear their intentions of reaching Shiganshina District and locating Grisha Yeager's basement which held the secrets of the Titans. Twenty-one trainees joined the Survey Corps that night, including Marley Warriors Reiner Braun and Bertolt Hoover. Their comrade Annie instead left to join the Military Police Brigade. The next day, the new recruits met Eren at the castle and informed him of Marco's death.
In the month following the Survey Corps acceptance ceremony, Eren remained under the watch of the Special Operations Squad as Hange performed various tests on Eren's Titan form. Tensions arose when Eren seemingly activated his Titan powers without permission, though it was later discovered that this event was in fact an effect of his Titan abilities. Hange concluded that not only was self harm necessary for Titan transformation, but also a fixed goal in the mind of the user.
During these weeks, other new members of the Survey Corps were trained in the strategy that would be implemented in the upcoming expedition: the Long-Distance Enemy Scouting Formation. In this formation, the Survey Corps soldiers on horseback would be spread across a great distance in a semicircular form divided into multiple columns. New recruits would be trusted with communications and spare horse maintenance. With this strategy, Scouts at the front of the formation would warn the formation of approaching Titans with red or black signal flares, depending on whether it is a common Titan or an Abnormal, respectively. Upon seeing the flare, the command group at the front of the formation would fire a green flare in the new direction in order to avoid contact with the Titan sighted.
Before the start of the expedition, Commander Erwin Smith revealed one of the hidden motives behind the expedition to the less-than-twenty surviving members of the Survey Corps from before the fall of Wall Maria. While the official purpose of the expedition would be to plot a new course from Karanes District in the east to Shiganshina District, Erwin had begun to suspect a Titan spy with powers similar to Eren was hiding within the military. Using the newly developed special target restraining weapon, the veterans planned to make use of the device to restrain and capture an intelligent enemy Titan should one infiltrate the expedition. For secrecy's sake, this plan was not made known to the Survey Corps soldiers outside of the survivors from five years prior, who could not have been spies.
For Eren Yeager's security, the Special Operations Squad was assigned to the center rear of the formation, the most secure position. In order to throw off intel for possible spies, other members of the Survey Corps were given false information concerning the location of the Special Operations Squad. Reiner Braun's plot of the formation claimed Eren was positioned up front in the right flank of the formation. Reiner relayed this information to Annie Leonhart, who was planning with her comrades to infiltrate the expedition and capture Eren.
In Karanes District, the Survey Corps' forces gathered in the early morning. Once all Titans beyond the outer gate had been drawn away, Commander Erwin Smith initiated the 57th Expedition Outside the Wall. The support team of the Survey Corps engaged in combat with approaching Titans as the main force of the expedition continued its advance.
Upon entering open territory, Commander Erwin initiated the Long Distance Enemy Scouting Formation. For a short time, the expedition went smoothly, with signals from the Scouts in the front lines properly reaching Erwin, who redirected the formation accordingly. However, at this time, Annie Leonhart as the Female Titan led a horde of Pure Titans into the frontal right flank, severely damaging the formation and slaughtering many soldiers while searching for Eren before any Scouts had a chance to fire a signal.
A short distance into the expedition, the Female Titan had infiltrated the formation as far as the second column of the right flank, where she quickly slaughtered Team Leader Dita Ness and his comrade Luke Siss. Armin Arlert, a member of Ness' team, was nearly killed as well, but upon cornering him Annie chose to spare him after lifting the hood of his cloak to determine his identity.
The Female Titan
Upon coming into contact with the Female Titan, Armin concluded that it must have been a human controlling a Titan similar to Eren. Armin was soon rescued by Reiner Braun, who joined him in pursuit of the Female Titan. The two were soon joined by Jean Kirstein, who fired off a signal flare to alert the formation of the Female Titan's appearance. Survivors from the right flank managed to send out signals at this time as well. While in pursuit with his comrades, Armin deduced that the Female Titan must be searching for Eren, who he concluded had likely been placed in the center rear where the formation is the most secure. After determining that it was their duty to delay the Female Titan's advance for as long as possible, the three soldiers engaged the Titan with their faces concealed by their hoods to increase the likelihood that they would be spared.
Armin was dismounted early in the fighting, and the Female Titan once again spared him. Upon seeing its face clearly, Armin deduced that the Female Titan may have been Annie Leonhart. As Jean engaged the Female Titan, Armin tested his theory by claiming that Eren, nicknamed "that suicidal blockhead," had been killed by the Female Titan. As Armin had predicted, the Female Titan halted its movements in reaction to his bluff. Reiner took the opportunity to close in on the Female Titan, pretending to go for a killing strike. The Female Titan caught Reiner in its grip, and Reiner used the moment to carve a message concerning Eren's location into Annie's hand. Jean and Armin thought for a moment that Reiner had been killed, but he soon escaped the Female Titan's grasp and retreated with Armin. Rather than pursuing them, the Female Titan followed Reiner's message and changed its course towards the center rear of the formation.
Shortly afterward, about an hour into the expedition, Commander Erwin Smith altered the course of the formation into the Titan Forest, suspecting that the chaos in the right flank was due to a Titan spy as he had predicted. Elsewhere, Armin, Reiner, and Jean were rescued and given new horses by Krista Lenz, a fellow recruit. Contrary to their expectations, the formation had begun to change course rather than calling a retreat altogether. As messengers from the right flank relayed the situation details to the center rear where the Special Operations Squad was advancing, the Female Titan had closed in on the center and wiped out Team Leader Darius Baer-Varbrun's forces.
Upon reaching the borders of the Titan Forest, Commander Erwin gave the order for only the central column wagon escorts, who were carrying the special target restraining weapons, to enter the forest while all other Survey Corps forces were to go around on either side. Some confusion spread among the other soldiers, though no one went against Erwin's orders.
The Titan Forest
Squad Levi followed the central wagon column into the forest as the remainder of the Survey Corps stood on guard at the outskirts of the forest, attracting several Titans without having orders to engage them. As Titans began to cluster at the outskirts of the Titan Forest, the Female Titan continued in its advance and came into contact with Squad Levi. Several soldiers had pursued her, though the Female killed all pursuers without slowing. Captain Levi fired off a sound grenade upon sighting the Female Titan, giving no orders to his panicking subordinates. Eren considered engaging in combat with his own Titan, but chose instead to trust Squad Levi and their captain's judgment. When the chase had progressed some distance into the forest, the Female Titan had been led into the special target capture weapon trap set up by the veterans. Upon Commander Erwin's orders, all weapons were fired and the Female Titan was successfully restrained.
While the soldiers of the Survey Corps speculated among themselves concerning what Erwin Smith's plan of action was, the veterans made several attempts to extract the human pilot from the nape of the Female Titan, only to discover that the Female had the ability to harden its skin to the point where blades were entirely ineffective. Commander Erwin ordered Keiji to prepare explosives to detach the limbs of the Female Titan, and Levi took the opportunity to intimidate the Female. Realizing that she was cornered, Annie used her Female Titan's scream to attract all the Titans in the area around the forest to her position. Erwin gave the order for all soldiers to defend the Female at any cost, but Annie succeeded in escaping unharmed from her Titan under the cover of the great amounts of steam emitted from her Titan and the falling Titans around her.
With the Female Titan lost, Commander Erwin gave the order for a retreat to Karanes District. Suspecting the Female Titan may still be active, Erwin ordered Captain Levi to replenish his blades and gas. Survey Corps leaders fired the appropriate signal flare for retreat, and Annie did the same. Thinking Annie's flare was Captain Levi's, Squad Levi changed course for her direction. When the squad had come into her sight, Annie struck down Gunther Schultz before transforming into the Female Titan a second time. Ordering Eren to continue in his retreat while they held off the Female Titan, Squad Levi engaged in combat. The three surviving soldiers succeeded in blinding and incapacitating the Female, but Annie prioritized her healing to her right eye in order to quickly regain her vision. When her eye had healed, she killed Eld Jinn as he came in for another strike. Before the others had time to react, the Female Titan stomped Petra Ral as Oluo Bozado struck her nape, only to discover her hardening ability all too late as the Female's kick killed him instantly. With his comrades dead, Eren transformed into his Titan and attacked the Female Titan.
Hearing Eren's Titan screams from afar, Mikasa Ackerman followed the voice while Captain Levi did the same having replenished his equipment. After a long and brutal fistfight between the Titans, Eren froze upon seeing a fighting stance that he recognized as belonging to Annie. In the brief opening, the Female Titan successfully defeated Eren's Titan and bit him out of the nape as Mikasa arrived at the scene. As Captain Levi followed, encountering the corpses of his squad, Mikasa pursued the Female relentlessly, striking from all angles in order to incapacitate her. Levi eventually caught up with Mikasa, and the two fell back a short distance in order to formulate a plan of attack. When their plan was decided, Mikasa advanced to distract the Female while Levi attacked from behind, blinding and crippling the Female Titan with extreme speed. Mikasa attempted to land a killing blow, but the Female made an attempt to strike at her. Levi prevented the attack, but broke his ankle in the process. The two succeeded in retrieving Eren, who had been kept in the Female Titan's mouth rather than being swallowed, and the three rejoined with the retreating expedition.
Around noon, the Survey Corps returned to Karanes District in defeat. Petra Ral's father met with Captain Levi upon their arrival and talked about Petra's possible wish to marry Levi, as Levi looked down with a defeated look. Political support and public opinion of the Survey Corps was heavily negative in response to their defeat, particularly with Commander Erwin Smith's responsibility for the heavy loss of life. All surviving members of the Survey Corps were summoned to Mitras with the order to hand Eren Yeager to the custody of the Military Police Brigade.
Upon their return to Wall Rose, Armin Arlert shared his suspicions of the Female Titan's identity with Commander Erwin. That night, Erwin called together a meeting between Levi, Eren, Mikasa, and Armin, in which he shared Armin's suspicions that Annie Leonhart was the Female Titan. They devised that in two days, the Survey Corps would commit a raid on Stohess District in order to capture Annie for questioning. Eren was visibly upset with the possibility of her betrayal, but nonetheless agreed to the operation.
While the majority of the Survey Corps traveled inwards from Karanes to Stohess, some members of the Survey Corps were assigned to keep watch on certain new recruits from the 104th Training Corps who were potential accomplices of Annie Leonhart. These soldiers and recruits would be absent from the planned Stohess District raid.