"Apocalypse Zero" is a dark and violent manga series set in a post-apocalyptic world where humanity faces extinction due to the emergence of monstrous beings known as the "Hakkeshu." These creatures, created through genetic experimentation, are led by the enigmatic and sadistic Kakugo, who seeks to dominate the remnants of the world. The story centers on Harara and Kakugo Hagakure, siblings who are the last of the Hagakure clan, a family of genetically engineered warriors designed to combat the Hakkeshu.

Harara, the protagonist, is a stoic and determined fighter who wields the "Apocalypse Zero" armor, a powerful and grotesque biomechanical suit that grants him immense strength and regenerative abilities. Despite his fearsome appearance and brutal combat skills, Harara is driven by a sense of duty to protect humanity and avenge his family. Kakugo, his sister, is a contrasting figure—psychotic, manipulative, and obsessed with destruction. She serves as both an antagonist and a tragic figure, her actions driven by a twisted love for her brother and a desire to surpass him in power.

The narrative unfolds as Harara battles the Hakkeshu and confronts Kakugo, who has allied herself with the monsters. The conflict between the siblings is central to the story, exploring themes of family, loyalty, and the consequences of unchecked ambition. The world-building is bleak and chaotic, with the remnants of society struggling to survive amidst the devastation wrought by the Hakkeshu. The series delves into the origins of the Hagakure clan and the experiments that created both them and the Hakkeshu, revealing a history of human hubris and moral corruption.

Throughout the series, Harara encounters various allies and enemies, including other survivors, rogue scientists, and members of the Hakkeshu. The battles are intense and graphic, showcasing the grotesque designs of the monsters and the brutal efficiency of Harara's combat style. The manga does not shy away from depicting the horrors of its world, with themes of body horror, mutation, and existential despair prevalent throughout.

"Apocalypse Zero" is a grim and unrelenting exploration of a world on the brink of annihilation, driven by the complex relationship between its central characters and the relentless action that defines their struggle. The series is notable for its dark tone, visceral imagery, and uncompromising portrayal of a dystopian future.