Primitive Desire

"The burning water, the land of ice... any of those. Anyone who saw those things would be the freest person in the world. Fight! Who'd value their life over something like that?"

- Eren explains his desire to leave the Walls

Gensho-teki Yokkyū (原初的欲求) is the 1st chapter of the 4th volume and the 14th chapter overall of the Attack on Titan manga, written and illustrated by Hajime Isayama.

Overview
While the soldiers are off fighting nearby Titans, Armin manages to wake Eren up from his dormant state in his Titan form. Soon enough, Eren proceeds to continue his mission. The sight of him carrying the boulder gives the Garrison elite soldiers hope, so they plan to continue defending him to ensure humanity's victory. After Mitabi and Ian meet their deaths, Eren succeeds in plugging the breach in Wall Rose. Rico shoots a yellow flare, signifying mission success. Unlike the other soldiers, Mikasa is only keen on leaving as soon as they retrieve Eren. Titans swarm behind them, but they are saved when Captain Levi comes to their rescue, heralding the return of the Survey Corps.

Summary
As the soldiers fight the onslaught of Titans drawn to Eren, Armin tries to bring him to his senses, reminding him of his desire to see the outside world. Slowly, Armin is able to bring Eren around in the nick of time. He asks Eren why he ever wanted to see the outside world despite all the dangers he would inevitably face, to which Eren responds that it is because he was born into this world. His senses regained, his Titan begins to rapidly regenerate from its wounds.

Elsewhere in the city, a single soldier remains under Rico Brzenska's command. As she orders a retreat, they stop at the sight of Eren carrying the boulder atop his shoulders. Mikasa and Ian Dietrich are also prepared to retreat until they spot Eren and the boulder. Armin approaches Ian's squad, informing them of their imminent success. With the mission now on its way to success, Ian commands his soldiers to protect Eren even if it costs them their lives.

In an attempt to get the Titans' attention off Eren, a small group under Mitabi Jarnach approaches the Titans on foot. The plan works, but puts them at a disadvantage when they need to escape. Ian orders his team to follow the others so they can hand the target over to them. Meanwhile, Eren's body feels like it's being crushed under the weight of the boulder. He sees Mikasa and Armin running on the ground and worries that they will fall prey to the Titans, and as Eren struggles with the stone and moves toward the hole, the soldiers are barely able to keep them away. While he marches towards the gate, Eren recalls Armin's question about the outside world and begins to think to himself.

"When we're born, all of us are free. People who reject that, no matter how strong they are, don't matter. The burning water, the land of ice... any of those. Anyone who saw those things would be the freest person in the world. Fight! Who'd value their life over something like that? It doesn't matter how terrifying the world is. It doesn't matter how cruel the world is. Fight! FIGHT! FIGHT!"

- Eren Yeager

Many soldiers die around Eren as he makes his way step by step towards the breach. Mitabi had been caught, and Ian is decapitated by a Titan who eats him. As one Titan manages to get right in front of Armin and Mikasa, Rico soars in and stabs it in the eye, allowing Mikasa time to get behind it and kill it. Armin looks over his shoulder and sees Eren is only a short distance away from the hole now. As Armin cries out in motivation, Eren seals the breach. Falling to her knees, Rico remarks everyone didn't die in vain. She fires the yellow flare, marking success.

Atop the wall, Pixis, seeing the flare, orders for reinforcements to immediately be dispatched. With the Titans moving towards them, Rico orders Mikasa to climb up the wall. She replies that she'll only withdraw after Eren is retrieved. Armin, now at the back of Eren's neck, tries to pull him free from the flesh of his Titan form. Mikasa asks about his condition. Armin informs her of his high fever and one part of his body still being stuck. Rico suggests cutting the limb off. After Rico slices at Eren's hands, Eren and Armin fall to the ground, nearly at the feet of two Titans. Mikasa rushes to their side, but cannot make it in time. As a Titan reaches out toward them, a soldier swoops in and dispatches both Titans. When the bodies fall, Eren manages to open his eyes and sees the emblem of the Survey Corps, the Wings of Freedom. The soldier, Captain Levi, turns to face the trainees, asking for the situation. On the other side of the wall, the Survey Corps ascends to join in the combat.

With the success of the mission, the Survey Corps and the Garrison Military Engineers hurried in and won the battle. Wall Rose is sealed, protecting everyone from the Titans again. They delight in humanity's first victory against the Titans, but acknowledge that it came with a high cost.