Executioner from Hell

Humanity's war against the Titans costs lives, blades, and cannon shells every time a giant approaches the gates. Hange Zoë answers that problem with the Executioner from Hell, sometimes called the Titan guillotine, a stationary killing apparatus that requires no combat at all. The prototype goes up at Trost District's southern gate, where its effectiveness is proven in front of an audience of reporters and soldiers.

Construction depends on Eren Yeager. The hardening power of his Titan form is essential to raising the structure, and after the trial run succeeds he volunteers to help erect additional units even though channeling that ability repeatedly leaves him drained and bleeding from fatigue. He accepts the toll gladly, reasoning that no one will ever have to be devoured again.

Two parallel mini-Walls jut out from the gate's exterior, spaced with bars so no Titan can squeeze through sideways. Above them, a pulley assembly anchored to the Walls suspends a massive log sheathed in metal. Teams of horses on the inner side haul the chains that hoist the log back into firing position after every drop.

The trap baits itself with a human. A lone soldier stands in the channel between the two barriers, and any Titan in the area closes in on the exposed target. The moment a Titan leans its head into the gap, the order is given and the log plummets onto its nape at lethal speed. Once the corpse evaporates enough to clear the channel, the horses reset the log and the cycle begins again.

During the public demonstration, a twelve-meter Titan wedges itself between the barriers, the log fires, and after a tense wait the kill is confirmed to celebration. Hange declares that Titans can now be exterminated without endangering anyone.

The Survey Corps operates the device, with Hange Zoë as its inventor and Eren Yeager as the indispensable builder whose hardening raised the structures. The wider Military plans a full deployment along the Walls to gradually purge every Titan trapped inside Wall Maria ahead of the reclamation campaign.

The plan works. Roughly nine months after its introduction, and a year on from the Battle of Trost District, the interior of Wall Maria is announced clear of Titans, opening Shiganshina District to resettlement just before spring. With the Walls later brought down by the Rumbling, the guillotines presumably do not survive either.