The Survey Corps launches its most ambitious operation to reclaim Wall Maria and reach the Yeager basement, which holds the secrets of the Titans. The battle at Shiganshina pits Erwin's forces against the Beast Titan, the Colossal Titan, and the Armored Titan in a desperate all-or-nothing confrontation. Commander Erwin leads a suicidal cavalry charge against the Beast Titan so Levi can land the killing blow, choosing to die so his soldiers can reach the truth. Armin sacrifices himself to burn Bertholdt out of the Colossal Titan, enduring incineration to give his friends a chance. Levi is forced to choose between injecting Erwin or Armin with Titan serum, ultimately reviving Armin. The basement is reached, revealing Grisha Yeager's photographs and documents that prove humanity exists beyond the walls in an advanced civilization.
The Survey Corps uses a coordinated charge across Shiganshina's rooftops, but the Beast Titan's accurate boulder throws devastates their formation before they can engage. Erwin leads a desperate decoy charge knowing every soldier will die, buying Levi the opening to slice the Beast Titan's nape. Bertholdt transforms into the Colossal Titan and unleashes a massive thermobaric explosion that incinerates everything within a half-mile radius. Armin outsmarts Bertholdt by exploiting the Colossal Titan's weakness after transformation, burning himself to cinders in the process. Hange captures a pair of Bertholdt's Titan-speaker warriors, gaining intelligence about Marley's military structure. The Survey Corps discovers the basement contents: photographs, a book of history, and Grisha's documents proving that the world beyond the walls is a complex modern civilization called Marley.
This arc delivers the long-awaited basement reveal that rewrites everything the audience believed about the Attack on Titan world. Erwin's death represents the end of an era for the Survey Corps, as the commander who drove humanity forward sacrifices everything for the truth. Armin's transformation into the Colossal Titan and Levi's agonizing choice between saving Erwin or Armin is one of the series' most debated and heartbreaking moments. The revelation that Paradis Island is actually a remote prison for Eldians, and that the world sees them as devils, transforms the entire moral framework of the story.