Thunder Spears

Ranks of Titans wait outside Shiganshina under the Beast Titan's command while Reiner scales the Wall on hardened fingertips. Erwin holds his attack, reading the field: a quadruped Titan beside the Beast carries cargo on a saddle, meaning it is intelligent, likely the scout that betrayed the Regiment's approach, and possibly not the only extra enemy in play. When the Beast Titan roars, the small Titans charge, and Erwin grasps the trap. The enemy means to slaughter the horses, stranding the Scouts deep in lost territory where they can simply be starved out; the big Titans arranged in a half-circle exist to pen them in.

Erwin stacks three squads at the gate to guard the mounts and assigns the Armored Titan to the squads of Levi and Hange, freeing their Thunder Spears for use as needed. Privately he re-tasks Levi to stay with the horses and take the Beast Titan's head when a chance appears, and he walks Armin through the rest of the scheme. Eren transforms inside the district and runs deeper into the town, presenting Reiner with an impossible choice between the horses and a Founding-Titan candidate who could escape to Trost under his own power. Reiner sees through the feint but chases anyway.

Eren, remembering that he has beaten Reiner once before, concentrates his hardening into the backs of his fists and cracks the Armored Titan's head plating, learning that focused hardening beats armor spread thin. Overconfidence costs him when Reiner seizes an ankle and slings him through a building. Meanwhile the gate defense flounders; recruits like Floch and Marlo get their first look at Titans, Levi mops up around them, and both he and Erwin silently register how badly the Regiment's veteran losses show.

A flashback reveals Erwin's private engine: he fights not for humanity but for his father's theory, and he has spent a career fooling comrades and himself into feeding sacrifices toward the basement and the truth Grisha Jaeger left there. Hange's earlier briefing introduces the Thunder Spear, an exploding lance built from technology the Interior Police had hoarded, made specifically because blades cannot hurt the Armored Titan.

When Eren throws Reiner off and creates the opening, Hange and Mikasa lead the strike, putting spears through both of the Armored Titan's eyes. The follow-up volley shreds the armor over his nape; Conny and Sasha freeze at the thought of finishing their old friend before Jean rallies them in. The episode cuts out on a panicking Reiner as a cluster of spears detonates against his exposed neck.

Episode 51 overall and the 14th of season three, a Wit Studio and Production I.G production directed by Akitoshi Yokoyama and Yasuhiro Akamatsu, written by Hiroshi Seko. Japanese broadcast came on May 6, 2019, the US airing on June 1, 2019. Source chapters are War on Two Fronts and The Thunder Spears within the Return to Shiganshina arc.

The information segment describes the Thunder Spear itself, likening its concentrated blow to a lightning strike, the comparison that gave the weapon its name in Hange's telling.