The Colossal Titan breaches Wall Maria's outer gate, and the Armored Titan smashes through the inner gate moments later, causing a catastrophic collapse of the outermost territory. Mass panic erupts as Titans flood into the Shiganshina district, consuming thousands of civilians in the evacuation chaos. Eren Yeager watches helplessly as his mother is carried away by a smiling Titan while soldiers forcibly drag him to safety. The Survey Corps launches a counterattack but suffers massive casualties against the unprecedented Titan onslaught. Paradis Island loses one-third of its total territory and approximately twenty percent of its human population in a single day.
The Colossal Titan's appearance atop Wall Maria triggers the evacuation of Shiganshina, but the Armored Titan's simultaneous destruction of the inner gate traps the fleeing population. Eren's mother Carla is crushed under debris and eaten by a Titan while Hannes, the family's friend, abandons his rescue attempt out of fear. Keith Shadis leads a desperate Survey Corps charge that results in devastating losses and proves the military is unprepared for coordinated Titan attacks. Grisha Yeager disappears shortly after the breach, leaving Eren with a basement key and a promise to learn the truth. Eren and his foster sister Mikasa are taken in by the military, and Eren swears a solemn oath to exterminate every Titan that exists.
This arc establishes the brutal reality of the Attack on Titan world and the existential threat Titans pose to human civilization. Eren's childhood trauma and his vow of vengeance become the driving motivation for his entire character arc across the series. The destruction of Wall Maria sets the stage for humanity's desperate struggle, the militarization of society, and the mysteries surrounding the Titans' true nature. Every major plot thread of the story traces back to this single catastrophic event.