Attack on Titan

Attack on Titan (Shingeki no Kyojin) is a dark fantasy action anime (2013–2023) adapted from Hajime Isayama's manga.

In a post-apocalyptic world, the last remnants of humanity live inside massive concentric walls (Maria, Rose, and Sina) to protect themselves from Titans—enormous, mindless, humanoid giants who devour people for no apparent reason and regenerate from almost any injury.

The story kicks off when the outermost wall is suddenly breached by the mysterious Colossal Titan, allowing Titans to flood in and devour countless civilians—including the mother of young Eren Yeager. Traumatized and furious, Eren vows to wipe out every Titan in existence. He joins the military along with his adoptive sister Mikasa Ackerman (a highly skilled fighter fiercely protective of him) and childhood friend Armin Arlert (a brilliant strategist with a deep curiosity about the world beyond the walls).

They eventually join the elite Survey Corps (Scout Regiment), the branch that ventures outside the walls to fight Titans and search for answers about their origins. The series starts as intense survival horror/action with brutal Titan battles, but evolves into a complex story about war, politics, freedom, morality, hidden histories, betrayals, and shocking revelations that completely flip the initial "humans vs. monsters" premise.

It's famous for its:
Jaw-dropping plot twists
High-stakes action and animation (especially the early seasons by Wit Studio)
Deep, morally gray characters
Exploration of heavy themes like genocide, oppression, cycles of hatred, and what it means to be "free"

The full series has 4 seasons (plus specials), and it's widely regarded as one of the greatest and most impactful anime ever made.

If you're just starting, the first season alone is a wild, gripping ride that hooks most people immediately.