Attack on Titan Season 1 is set in a world where humanity is on the brink of extinction, living in fear of giant humanoid creatures known as Titans. These Titans have forced the remnants of human civilization to take refuge within three massive concentric walls: Wall Maria, Wall Rose, and Wall Sina. The story begins in the year 845, when the Colossal Titan, an enormous and powerful Titan, suddenly appears and breaches Wall Maria. This breach allows Titans to invade the district of Shiganshina, leading to the destruction of the town and the deaths of many residents, including Eren Yeager's mother. Eren, along with his closest friends Mikasa Ackerman and Armin Arlert, barely escape the carnage and are evacuated to safety behind the next wall. Traumatized and fueled by anger, Eren vows to kill every Titan and reclaim the world for humanity. The series then follows Eren, Mikasa, and Armin as they join the military to fulfill Eren's vow. They undergo rigorous training and eventually graduate, joining different branches of the military: Eren joins the Scout Regiment, known for their dangerous expeditions outside the walls; Mikasa, driven by her protective instincts towards Eren, follows him into the Scouts; and Armin, despite his self-doubt, joins the Scouts as well due to his strategic mind. During their first mission outside the walls, Eren's squad faces devastating losses at the hands of the Titans. In a desperate attempt to save his friends, Eren is seemingly killed by a Titan, but it's soon revealed that he possesses the ability to transform into a Titan himself. This revelation shocks both his comrades and his enemies, raising questions about the true nature of the Titans and Eren's origin. Despite the initial fear and distrust from his fellow soldiers, Eren is eventually allowed to use his Titan form to aid humanity's fight against the Titans. The military decides to use Eren's Titan ability in a risky operation to seal the breach in Wall Maria. During this mission, Eren struggles to control his Titan form but ultimately succeeds in plugging the hole with a massive boulder, proving his value to humanity. However, this victory is overshadowed by the emergence of a new threat: the Female Titan, a highly intelligent and deadly Titan who specifically targets Eren. The Scout Regiment embarks on a mission to capture the Female Titan, leading to a series of intense battles. It is eventually revealed that the Female Titan is actually Annie Leonhart, one of Eren's former comrades. Annie is part of a mysterious group with the ability to transform into Titans, who have infiltrated the military for unknown purposes. In a climactic battle within the walls of the city, Eren confronts Annie, and after a brutal fight, she encases herself in an impenetrable crystal to avoid capture and interrogation. The season ends with the characters left with more questions than answers. They begin to realize that the truth about the Titans and the world they live in is far more complex and sinister than they had imagined. The final shot of the season shows a crack in Wall Sina, revealing the face of a hidden Titan within the walls, hinting at the dark secrets that lie ahead.