"Exoskull Zero" is a science fiction manga set in a dystopian future where humanity faces extinction due to the emergence of biomechanical creatures known as "Hollows." These creatures, born from a mysterious energy source called the "Zero Core," have overrun the planet, forcing survivors to take refuge in fortified cities. The story centers on Kael Ardent, a former soldier turned mercenary, who pilots an advanced exosuit known as the Exoskull Zero. This exosuit, powered by fragments of the Zero Core, grants its wearer immense strength and unique abilities but at the risk of destabilizing the user's mind.

Kael's journey begins when he is hired to escort a young scientist, Dr. Lina Voss, to a remote research facility. Lina claims to have developed a weapon capable of destroying the Hollows and ending their reign. However, their mission is complicated by rival factions, including the militaristic Iron Dominion and the rogue scavenger group known as the Black Talons, all vying for control of the Zero Core's power. As Kael and Lina navigate treacherous landscapes and face relentless Hollow attacks, they uncover deeper secrets about the Zero Core's origins and its connection to humanity's downfall.

The narrative explores themes of survival, sacrifice, and the ethical dilemmas of wielding immense power. Kael struggles with the psychological toll of using the Exoskull Zero, which amplifies his emotions and memories, often blurring the line between reality and hallucination. Lina, driven by guilt over her role in the Zero Core's development, seeks redemption by completing her weapon, even as she questions whether humanity deserves a second chance. Supporting characters, such as the enigmatic hacker Jax and the hardened mercenary leader Rhea, add depth to the story, each grappling with their own motivations and moral conflicts.

The plot intensifies as Kael and Lina discover that the Hollows are not mindless monsters but the result of a failed experiment to merge human consciousness with the Zero Core. This revelation forces them to confront the possibility that the Hollows may hold the key to humanity's survival, challenging their mission's purpose. The manga balances action-packed sequences with introspective moments, creating a layered narrative that examines the consequences of technological advancement and the fragility of human morality in the face of extinction.