In the monster-plagued kingdom of Marukido, two sisters, Layla and Laura, share a close bond. Their peaceful life is shattered when Layla, due to her unique status as a Saint vital to the nation's security, is sacrificed through a conspiracy by wicked nobles. Desperate to rescue her older sister, Laura vows revenge against the kingdom that betrayed them.

The narrative follows Laura’s transformation from an ordinary girl into a formidable warrior known as the Revenge Princess. Her quest for vengeance forces her down a dark and violent path. She seeks out the Demon King with the intention of destroying her ultimate enemy. Upon finding the Demon King, Laura cannot defeat him. Instead of accepting defeat, she makes a pivotal choice to join the Demon King's army, redirecting her destructive power back at the kingdom of Marukido itself.

Laura is the protagonist, driven by an intense and unwavering obsession to save her sister from being frozen as a sacrifice for the state. She is depicted as exceptionally strong-willed and physically powerful, capable of taking on numerous enemies in direct combat. Her defining trait is her absolute refusal to give up on her sister, leading her to abandon her homeland and ally with demon forces. Layla is the elder sister whose capture serves as the catalyst for the entire plot. The Kingdom of Marukido is the initial setting, a nation plagued by monsters where the nobility is corrupt enough to sacrifice its own citizens for political gain. The Royal Family, particularly the crown prince, is portrayed as antagonistic, contributing to the kingdom's moral decay.

Key narrative arcs include Laura’s initial attempts to fight the kingdom through conventional means, which prove futile. The story takes a significant turn when she confronts the Demon King. Rather than a climactic battle to save the world, Laura fails to defeat him, leading to the most notable arc where she joins the monster forces to wage war on humanity in order to achieve her personal goal. Subsequent volumes focus on her battles against the kingdom while navigating her new alliance with the demon realm. Despite the grim premise, the narrative suggests that Laura is not entirely alone, as family members remain supportive of her crusade.