A century and a half after the Demon King was sealed away by the hero, the demon realm has fallen into ruin. The former demon lord’s subordinates, now leaderless and demoralized, spend their days in idle decay, while human adventurers regularly raid their lands for sport and profit. The official demon realm bureaucracy, however, continues to operate on obsolete wartime protocols, still processing forms and requisitions for a war that ended long ago. Into this stagnant world steps Mephisto, a high-ranking demon who once served as the Demon King’s chief strategist. Rather than seeking revenge or attempting to revive his master, Mephisto is tasked with the unglamorous duty of postwar administration: settling outstanding debts, decommissioning magical weapons, managing refugee claims from monster tribes, and renegotiating territorial borders with the human kingdoms. His mission is to formally conclude the war and liquidate the Demon King’s remaining assets so that the demon realm can move forward.

Mephisto is a calm, calculating, and perpetually weary fox-eared demon who prefers spreadsheets to swords. He is accompanied by Iris, a young and impulsive human girl who was raised in the demon realm after being abandoned as a child. She serves as his assistant and moral compass, often challenging his cold pragmatism with emotional appeals. The central conflict arises from the fact that not everyone wants the war to end. Hardline demon generals, who grew powerful on wartime plunder, resist Mephisto’s disarmament policies. Human noble houses, who profit from border skirmishes, secretly fund insurgent groups to keep the conflict simmering. Meanwhile, the sealed Demon King’s consciousness occasionally manifests through cursed relics, whispering temptations to both demons and humans who crave his return. Mephisto must navigate these factions while also confronting the personal cost of his duties, as his own past includes dark orders he carried out during the war, orders that Iris and others are only beginning to uncover.

The narrative unfolds through episodic arcs that each tackle a specific postwar problem. In the first major arc, Mephisto travels to the human capital to sign a formal peace treaty, only to discover that the hero who sealed the Demon King has vanished, and the current king is a puppet controlled by war-hawkish ministers. This forces Mephisto into backchannel diplomacy with the hero’s former companions, now elderly and disillusioned. A middle arc focuses on a cursed forest that was once a battlefield, where the lingering resentment of fallen soldiers has manifested as undead creatures. Mephisto must decide whether to purify the forest, which would erase the memories of the dead, or preserve it as a memorial, which would continue to threaten nearby villages. A later arc reveals that the Demon King’s seal is weakening not because of external attacks, but because the bureaucratic neglect of the demon realm has caused the magical infrastructure supporting the seal to decay, forcing Mephisto to choose between maintaining the seal and diverting resources to famine relief.

The primary cast includes Mephisto’s rival, General Garm, a boar-like demon who leads the opposition faction and believes that only a return to conquest can restore demon pride. Garm is not evil but is trapped in a warrior’s mindset, unable to imagine peace as anything other than surrender. On the human side, Sister Agnes, a high-ranking church inquisitor, initially hunts Mephisto as a heretic but gradually becomes an uneasy ally as she realizes that the church’s own leadership is manipulating the conflict to consolidate power. There is also the mysterious archivist, Lich Kreiss, who has served every demon lord for millennia and holds the true records of how the war began, records that implicate both demon and human elites in a conspiracy that prolonged the fighting for their own benefit. Kreiss offers Mephisto information only at the cost of favors that often complicate his mission further.

As the synopsis progresses, Mephisto uncovers that the original hero did not seal the Demon King out of righteousness, but because the Demon King had discovered a secret that would have collapsed the political order of both realms. The hero and the Demon King had actually been negotiating a joint peace when a third party assassinated the hero’s family and framed the demon realm, forcing the hero to act. The seal was therefore a desperate compromise, not a victory. This revelation forces Mephisto to rewrite the official history, a move that alienates him from both demon hardliners and human nationalists. In the final narrative arc, Mephisto proposes a radical solution: instead of maintaining the seal or breaking it, he will transfer the Demon King’s consciousness into a new vessel—himself—so that the king can personally sign a surrender and abdication, legally ending the war. This act would erase Mephisto’s own identity, but it is the only way to satisfy both realms’ legal frameworks.

The climax sees Mephisto undergoing the ritual while Iris and his allies defend the ceremony site from a coalition of warmongers from both sides. The transfer succeeds, but the Demon King’s personality does not overwrite Mephisto; instead, they merge, creating a new entity that possesses Mephisto’s administrative skills and the Demon King’s ancient wisdom. This new ruler immediately dissolves the demon realm’s feudal military structure, declares all territorial claims null, and offers the demon population citizenship in the human kingdoms under a mutual aid treaty. The final chapters follow the messy, often comedic implementation of this integration: demons working as farmhands, former generals attending anger management therapy run by Iris, and Mephisto—now a blend of king and bureaucrat—personally approving building permits for mixed-species villages. The ending is not a triumphant victory but a quiet, ongoing effort to clean up the aftermath of a war that nobody truly won, with the understanding that true peace is not a single event but a daily, tedious, and necessary chore.