"I'm Quitting Heroing" is a fantasy anime series that centers on Leo Demonheart, a former hero who, after saving the world from the Demon King, finds himself ostracized by humanity due to his overwhelming power. Unable to integrate into society, Leo seeks refuge with the Demon King's army, now led by the Demon King's daughter, Echidna. The series explores Leo's attempts to adapt to his new life among former enemies while grappling with his identity and purpose.

The narrative begins with Leo joining the Demon Army, where his unparalleled strength and strategic genius quickly elevate him to a leadership position. However, his presence disrupts the army's dynamics, as his methods clash with the traditional ways of the demons. Echidna, the pragmatic and resourceful commander, initially views Leo with suspicion but gradually recognizes his value in strengthening the army. The story delves into the complexities of coexistence, as Leo's human perspective challenges the demons' worldview, and his efforts to reform the army lead to both comedic and dramatic situations.

Key characters include Leo, whose internal conflict between his heroic past and his current role drives much of the narrative. Echidna serves as a foil to Leo, balancing her responsibilities as a leader with her growing respect for his abilities. Supporting characters, such as the loyal demon soldiers and former human allies, add depth to the story, highlighting themes of redemption, trust, and the blurred lines between good and evil. The series blends action, humor, and introspection, creating a multifaceted exploration of its central premise.

The plot progresses through a series of episodic challenges, as the Demon Army faces external threats and internal strife. Leo's innovative strategies and unconventional approach to leadership often lead to unexpected outcomes, forcing both humans and demons to reconsider their preconceptions. The series also touches on the consequences of war, the nature of heroism, and the possibility of reconciliation between opposing factions. By the end, "I'm Quitting Heroing" presents a nuanced portrayal of its characters and their evolving relationships, offering a fresh take on the traditional hero-versus-demon narrative.