Hugo has been trapped in a time loop for six consecutive lives, each one ending the same way: with him being murdered by a member of his own family. With each reset, he retains the skills and knowledge from his previous existences, becoming a master of assassination, strategy, and other arts, yet he remains unable to escape his grim fate or form a meaningful connection with another person. At the start of his seventh life, he abandons any hope of a peaceful existence and swears a solemn vow of revenge against his treacherous relatives. Seeking the power to destroy his family or a swift end to his suffering, he approaches the powerful archduke's daughter, a young woman rumored to be a bloodthirsty monster in human flesh, and offers to become her servant or her groom.

The princess, Meltreza, is indeed a monster, but she is also the most beautiful woman Hugo has ever seen. Possessing the ability to instantly detect sincerity in others, she recognizes that Hugo is telling the truth when he confesses the story of his previous six lives and his desire for revenge. Rather than recoiling, she is moved by his perseverance and immediately accepts him, forming an instant and powerful bond. Their relationship quickly deepens into a conspiratorial and romantic partnership, with the pair adopting pet names for one another and working in perfect sync. Meltreza possesses the powers of her monster lineage, including a magical eye that can unlock the hidden potential within Hugo, granting him even greater strength and ability. Her grandfather, the toughest and most formidable warrior in the kingdom, also takes a liking to Hugo and trains him to become an even more lethal fighter.

The central narrative arc follows Hugo and Meltreza as they systematically confront everyone who has wronged them. Meltreza uses her authority and cunning to make Hugo's scheming family squirm, exposing their treachery and putting them in their place. Meanwhile, Hugo hones his new skills to become capable of facing any physical threat. The story unfolds as a power and revenge fantasy, with the pair cutting a swath through a world populated by cartoonishly evil villains, from Hugo's own murderous relatives to other antagonists in the kingdom. The seventh life becomes a decisive break from all that came before, as the birth of their partnership truly intertwines their fates, and Hugo finally finds happiness and a reason to live beyond simple vengeance.