In 2327, the world is unified under the United Sovereign World (USW), a federal state where advanced technology brings convenience to all. Cultural and linguistic differences persist, but disparities in most fields have narrowed, nearing a utopian ideal. Yet, this harmony fractures as terrorism—driven by clashing religions and ideologies—erupts with bombings, city-crippling hacks, and biochemical attacks. The USW declares war on these relentless threats.

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A deadlier crisis soon overshadows the terror: spontaneous combustion. People ignite without warning—hands, faces, then their entire bodies—burning to nothing, leaving no ash. The flames spread like contagion, consuming nearby organisms in a chain reaction. First recorded in September 2325, a 21-year-old man ignited in an indoor pool, triggering a cascade that incinerated 11 others. Despite being soaked, they burned completely, yet the water and building remained untouched. Within two years, 200 lives are claimed.

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The USW’s national agency, Seraph, uncovers the cause: a parasite named "Kaladon." It infects humans, reproduces, and spreads to others. When it dies, it drains its host’s moisture, lowering their ignition point to spark instantaneous combustion. If one parasite dies, its offspring and their hosts burn too, amplifying the devastation.

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To counter this, the USW forms the elite "Punisher" task force. Publicly, they’re said to eradicate Kaladon and protect hosts. In truth, they identify combustion triggers, execute infected hosts, and harvest the parasites for research. This ruthless approach births a new threat: some parasites evolve, merging with hosts to survive. These "Flames" neither die nor relent, burning cities alongside their hosts until the parasite’s end. The USW deploys Punishers to eliminate them.

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Amid terrorism, Seraph’s deception, and the escalating combustion crisis, one individual joins the Punishers, stepping into a web of secrets tied to Kaladon.