The Thunder Spears

Kaminari Yari (雷槍) is the 2nd chapter of the 19th volume and the 76th chapter overall of the Attack on Titan manga, written and illustrated by Hajime Isayama.

Overview
While Levi tries to protect and coordinate the new Survey Corps recruits, Erwin finds himself tempted to abandon his soldiers in order to reach Eren's basement and finally discover the secret to the world that his father had once tried to find. On the ground, Eren and Reiner continue to face off, with Eren employing his new hardening abilities to effectively fight Reiner. Realizing that he cannot hope to beat Eren on his own, Reiner prepares to take a different approach to kidnapping Eren, but is blindsided by Hange's squad, and crippled by their new weapon, the Thunder Spears. Blinded and unable to fight back, Reiner is powerless to stop Hange's squad from using their spears to destroy his nape, and is engulfed by the explosion caused by their weapons.

Summary
Marlo's squad is ordered to retreat west with their horses and protect their fellow recruits in Squad Dirk. As Marlo tries to determine where to leave the horses in order to engage the Titans, he is alarmed to see two Titans approaching from the east. The recruits are saved by Levi, who orders Marlo's squad to take care of their duties before the Beast Titan makes his move.

As Erwin watches the battle unfold from atop Wall Maria, he notes that the Survey Corps is not as powerful as it once was. Erwin begins to reminisce about his early years in the Corps, remembering how he would tell his fellow recruits about his father's theories. However, soon after joining the Corps, Erwin had realized that he was the only person who had joined the Corps for his own sake, while all of his fellow recruits had joined the Corps for the sake of humanity. Soon after joining, Erwin had his own troops to command, and by telling them to devote their lives to humanity, he fooled not only them, but himself, and leading to the deaths of many Corps members. As Erwin pictures the bodies of those who have died fighting the Titans, he considers trying to reach Eren's basement to discover the secret Grisha Yeager kept hidden even if Corps' plan backfires.

Eren continues to beat Reiner back, using his hardening ability to harden his fists and allow him to smash through Reiner's armor. However, Reiner manages to gain the upper hand, slinging Eren into a nearby building. Reiner attempts to crush Eren's head with a single punch, but Eren manages to dodge it. As they look on, Hange instructs Mikasa to wait for their squad to surround Reiner before attacking him.

In a flashback, Hange unveils the Corps' new weapon, the Thunder Spears, to the recruits. Hange explains that the spears were designed using technology taken from the Military Police Brigade, and that they will hopefully prove effective against Reiner's armor, as the Corps' blades are useless against it. Hange reminds the recruits that the main goal of their expedition is not only to plug the hole in Wall Maria, but to kill Reiner and Bertolt, and that it will be difficult to do so with only Eren's new hardening abilities. A question from Mikasa prompts Hange to volunteer to demonstrate the weapons' abilities to the recruits. Outside, the recruits are shocked by the Thunder Spears' explosive power. As the recruits wonder if the new weapons will be enough to defeat Reiner, Hange admits that the weapons have one weakness...

As Eren and Reiner continue to fight in the present, Eren manages to throw Reiner away. Reiner speculates that he won't be able to kidnap Eren on his own, and decides that he will have to take a different approach. However, before he can make his move, Hange and Mikasa attack, surprising Reiner. Bewildered, Reiner wonders what the soldiers can do to hurt him, as their weapons cannot cut through the armor that completely covers his body. By the time Reiner realizes that Hange and Mikasa are wielding new weapons, it is too late for him to move, and he is blinded by the two, who fire their Thunder Spears directly into his eyes. As Mikasa and Hange retreat, they detach the Thunder Spears from their 3D maneuver gear, and the spears lodged in Reiner's eyes explode.

As Reiner doubles over in pain from the Thunder Spears, Hange looks on, noting that the Thunder Spears' only weakness is that they can only be used in areas with high objects that can be used as an anchor for their Three Dimensional Maneuver Gear, as anchoring their gear in the Titan they attack would only result in them being caught up in the explosion as well. The rest of Hange's squad approaches Reiner's Titan Form, firing their Thunder Spears into the armor on its nape. The resulting explosion strips away Reiner's armor, and completely exposes its nape for attack. Hange orders the squad to attack once more, but Sasha and Connie are left frozen in place at the thought of killing their former comrade. They are only convinced to join the final attack on Reiner by Jean, who reminds them that they were already prepared to face this outcome. As the entire Squad fires their Thunder Spears into the Armored Titan's nape, Reiner is afforded only enough time to quietly plead for them to wait before being engulfed in an explosion.