|What are you really?! Human?! Or Titan?!|
|— The Garrison captain interrogates Eren|
Whereabouts of His Left Arm: The Struggle for Trost, Part 5 (左腕の行方 ―トロスト区攻防戦⑤― Hidariude no Yukue -Torosuto-ku Kōbōsen (5)-?) is the 9th episode of the 1st season and the 9th episode overall of the Attack on Titan anime, produced by Wit Studio and Production I.G.
The Scouts on a scouting mission beyond Wall Rose receive news of the attack on Trost, and Commander Erwin orders for an immediate retreat. Meanwhile, Eren is brought before the leaders of the Garrison to answer for his sudden Titan powers.
Eren attempts to convince the captain that he is human, but his words fall on deaf ears. When the captain orders the artillery crew to fire upon Eren, he transforms into a partial Titan to shield his friends from the blast.
Before the Colossal Titan breaks through Wall Rose, the Scout Regiment departs on their latest expedition. Among the townspeople, Eren, Mikasa, and Armin watch their departure. One of the townspeople spots Captain Levi, and then says that in battle, he is as mighty as an entire brigade. Levi, hearing this, gets a little irritated. Squad Leader Hange Zoë makes a joke that they would be heartbroken if they knew how much of a clean freak he was.
Before leaving, Hange imagines what kind of Titans she will see. She hopes that they meet some Abnormal ones and Levi comments that he can already see one which makes Hange search around. Levi then pats her and says to her that the Abnormal one is right here, in front of him.
The soldiers entrusted with the mission this time are mankind's best and brightest soldiers. Even so, when troops advance into Titan territory, the casualties still exceed thirty percent. While out for the mission, one of the soldiers is caught by a Titan. Half inside the Titan's mouth, he threatens it, saying that humans will exterminate them, particularly Captain Levi. As he says this, Levi shows up and disposes of the Titan. With reinforcements arriving, he orders Petra to take care of the wounded soldier. He then orders the rest of them to assist in killing a Titan to the right, while he takes two Titans, alone on the left.
Elsewhere, Hange enjoys the mission. She confronts one of the Titans, and then says that she will not hurt it at all. The Titan ignores Hange's words and tries to grab her, but Hange quickly dodges and cuts its nape. She then lands on the ground, while asking the Titan if her attack hurts it.
As Levi approaches the two Titans on the left, he thinks to himself that they all possess the same ridiculous faces. He easily kills them but had blood stained on his hands when he finishes off the second Titan, causing him to take pause and immediately clean it up. Taking a short break, he rejoins Petra and the soldier he saved earlier. The soldier, with his last breath, asks Levi if he had been useful. Encouraging him, he takes the soldier's hand and tells him he has done more than enough and his spirit will stay with him and makes him stronger, which allows him to die in peace. Commander Erwin approaches them on horseback, informing them that they must retreat. Levi and Petra are shocked when Erwin informs them that the Titans are moving north - towards the city. Worried that the Wall may already be breached, they leave.
As Eren is swallowed whole by a Titan right in front of Armin, the mouth bites down, tearing off Eren's left arm. Now in the Titan's stomach, Eren is surrounded by fellow dead or dying soldiers, one whispering that she misses and wants her mother, before sinking into the stomach acid. In disbelief, he remembers all of his training and how he is changed these past five years. He begins to remember his own mother. Questioning why the Titans took everything from him, he again swears he will destroy them all, with his bare hands.
Eren, growing even more desperate and despairing, reaches towards the Titan's throat with his missing arm. Then, suddenly, an enormous arm explodes out of the Titan's mouth, causing it to stumble stupidly, before falling face first. As the Titan lay on the ground, Eren emerges in Titan form from the Titan's back as it rips apart. Desperate for revenge, Eren decapitates the Titan that ate him with a powerful stomp before attacking a smaller Titan with one punch to its mouth, damaging its head enough to kill it. He stomps on the deceased Titan's head repeatedly, consumed with bloodlust to kill all of the Titans.
Eren wakes up, having remembered these events in his sleep, muttering his desire to kill. He then notices the frightened and misunderstanding Garrison soldiers, who want to kill Eren, as they believe that he is a Titan who wants to devour them all. As the situation heightens, Eren appears to have no recollection of his time as a Titan.
Inside Wall Rose, Conny explains how they were able to refill their gas and escape from Trost with Christa, her friend, and the other soldiers. Christa asks about the rest of the soldiers that are not there, and Conny announces their dooms with a mournful expression. Christa's friend questions Mikasa's whereabouts, and Conny replies that he thinks Mikasa has come back late with Jean. She asks Jean if Mikasa was wounded, but Jean refuses to answer it, saying that he has sworn to keep it secret from the others, but believing that soon everyone will know it.
On top of the Wall, Captain Hannes talks about the new defense plan the technical crew created, but they still cannot let their guard down. When he reads the distress on his comrade's face, he asks what is wrong with him. His comrade answers that he is concerned about his friends that stayed in the vanguard. Hannes encourages him to stay focused on the interception, but then his comrade asks about Eren, Mikasa, and Armin because he heard they also remained in the vanguard. He apologizes for talking too much, but Hannes says that he believes in them due to their individual abilities.
Meanwhile, an ever-confused Eren is given a difficult situation: if he says something the captain considers deceitful or move even an inch, a cannon is ready to shoot him anytime. Then, the captain questions him, asking if he is a human or a Titan.
Not understanding, Eren asks what he means. Losing patience, the captain states that there were numerous witnesses that saw him coming out of the Titan, which in effect, makes him the enemy. Not wanting to risk any more soldiers, a soldier suggests that they kill him while he is still in human form.
Mikasa overhears him, and threatens to brutally kill anyone who tries to harm Eren. Another soldier informs the captain that Mikasa is one of their best soldiers, and it would be a great loss if she were slain. While Armin suggests fleeing, Eren struggles to remember what has just transpired. He looks at his left arm, and he starts to realize that what he saw was not just a dream. When the captain asks again what he is, Eren knows that his answer affects his friends as well. Eren answers that he is human, but the captain does not buy it, and orders the cannons to fire on his command. Mikasa grabs Eren, and Armin, and tells them to flee.
At that exact moment, Eren witnesses his father's key coming out from his shirt. Looking at it, Eren recalls him giving him the key, telling him to keep it on him at all times, and then giving him an injection that damaged his memories of that moment. Then he remembers the basement of his former home, with his father saying that although it would be an insanely dangerous journey, they would have everything they would ever need to destroy the Titans, once and for all. He assures Eren that "their memories" will be able to teach him how to use his new powers.
Time seems to slow down as he recalls his father telling him that if he wishes to protect Mikasa and Armin, he must master his new power. With this, Eren instinctively bites down on his hand and appears to catch the cannonball. When the smoke partially clears, it is shown that Eren has partially transformed into a Titan thus terrifying everyone within range but he did, in fact, save Armin and Mikasa by stopping the cannonball with the Titan's hand.
Currently Publicly Available Information
The Current Scout Regiment
Their primary mission consists of reconnoitering outlying areas. Their objectives have changed following the fall of Wall Maria.
After the fall, their new objective is to prepare for the second operation to recapture Wall Maria by establishing supply points and routes for troop movement.