Takeshi Ōmura, a middle school student, bears an extreme curse of misfortune inherited from his father, the former "god child." This affliction subjects him to constant, severe bad luck, enduring calamities like his house burning down, frequent accidents, and fatal incidents such as a concussion leading to death. After dying, he encounters Elle, an angel dispatched as his guardian. Elle resurrects him and reveals the curse's origin. Takeshi initially attempts to transfer the curse by sealing it into a ball, but reclaims it to protect a young girl endangered by it. This selfless act causes Elle to become human so she can remain constantly near him, as her presence lessens his bad luck. Elle moves into his home, posing as his stepsister, and attends his school.

Following the loss of his home, Takeshi lives with his aunt Sanae Ōmura and cousin Motoko Eguchi. His father, Takashi Ōmura, abandoned him at age five, contributing to his difficult childhood. Takeshi's family relationships are strained; Sanae is caring but often comically imposes feminine clothing on him, while Motoko ridicules him and displays ambiguous romantic interest. His mother, Ruelle, was an angel assigned to his father, making Takeshi a half-angel hybrid. This heritage connects to Elle's background, as Ruelle is also Elle's mother, making them half-siblings. This connection creates complex dynamics, including near-incestuous encounters where Takeshi and Elle briefly consider having a child before acknowledging their emotional unpreparedness.

Takeshi's life becomes entwined with supernatural conflicts, facing threats from demons like Isra, Elle's twin sister who turned demonic after their mother's death. His relationships include Hikaru Hoshino, a half-demon childhood friend and kendo champion, and her sadistic sister Michiru. Takeshi develops romantic involvements with both Elle and Hikaru, forming a love triangle where both vie for his affection. Later, he fathers a daughter, Prayer, with Elle through an immaculate conception; Prayer hatches from an angel's egg but dies due to Elle's powers being depleted from repeatedly resurrecting Takeshi. Prayer's soul survives within Takeshi and Elle, enabling eventual resurrection.

Throughout his journey, Takeshi evolves from resenting his cursed circumstances to embracing resilience and protectiveness. Key events include participation in a tournament arc where demons kidnap him to coerce Elle and others into combat, and confronting revelations about his family's celestial and demonic ties. His development culminates in accepting his role in balancing cosmic forces of good and evil, navigating themes of sacrifice, parental abandonment, and identity amidst supernatural turmoil.