To experience the full story chronologically, follow this order: Season 1 (Episodes 1-25), OADs (especially 'No Regrets' for Levi's backstory and 'Ilse's Notebook'), Season 2 (Episodes 26-37), Season 3 Part 1 (Episodes 38-49), Season 3 Part 2 (Episodes 50-59), The Final Season Part 1 (Episodes 60-75), The Final Season Part 2 (Episodes 76-87), and finally The Final Season: The Final Chapters (Special 1 & 2).

The Nine Titans are unique powers passed down through Eldians: Founding Titan (controls Titans/memories), Attack Titan (sees future memories), Colossal Titan (massive size/steam), Armored Titan (hardened armor), Female Titan (versatility/mimicry), Beast Titan (animalistic/throwing), Jaw Titan (speed/crushing power), Cart Titan (endurance/utility), and War Hammer Titan (structural hardening creation).

The three walls—Maria, Rose, and Sina—were created by King Fritz using the hardening power of millions of Colossal Titans. They were built to protect the remnants of Eldian humanity on Paradis Island from the Pure Titans roaming outside and to isolate them from the rest of the world, serving as both a shield and a potential doomsday weapon (The Rumbling).

Eren Yeager is the series' complex protagonist who starts as a vengeful boy wanting to kill all Titans but evolves into a morally ambiguous figure. As the holder of the Attack and Founding Titans, he orchestrates the Rumbling, a global genocide, believing it is the only way to guarantee freedom for his friends and Paradis Island, making him both hero and villain.

The Rumbling is a cataclysmic event where the millions of Colossal Titans hidden within the three Walls are released to march across the earth. Triggered by the Founding Titan, it is designed to flatten the entire world and destroy all life outside Paradis Island, serving as the ultimate deterrent and weapon of mass destruction.

The anime is largely faithful to Hajime Isayama's manga, but there are differences. The anime reorders the training arc in Season 1 for better pacing and cuts some political dialogue in Season 3. Crucially, the anime finale features extended dialogue between Eren and Armin that clarifies Eren's motivations and regret, which was a direct response to criticism of the manga's ending.

The source of all Titan power is the Source of All Living Matter (often called the 'Hallucigenia' or 'shiny centipede'). It bonded with a young slave girl named Ymir Fritz 2,000 years ago, granting her the power of the Founding Titan. After her death, her power was split into the Nine Titans, and her descendants (Subjects of Ymir) can be turned into Titans via spinal fluid injection.

Pure Titans (mindless Titans) are driven by a singular, instinctual nightmare to find and consume a Titan Shifter (a human possessing one of the Nine Titans). If a Pure Titan eats a Shifter and consumes their spinal fluid, they regain their human form and consciousness, inheriting the Shifter's power. They eat humans indiscriminately in the subconscious hope of ending their nightmare.

The Ackerman clan (Mikasa, Levi, Kenny) was the result of Titan science experiments. They possess the physical strength and combat instincts of a Titan while remaining in human form. They can also access the battle experience of all their ancestors via 'Paths' and are immune to the Founding Titan's memory-wiping abilities.

The ending is bittersweet and tragic. While the Titan curse is erased from the world and Eren's friends survive to live long lives, 80% of humanity is wiped out by the Rumbling. The story concludes with themes of the cyclical nature of war, suggesting that while peace was achieved for a time, conflict is an inevitable part of human nature.