Takigawa Yuma, a high school third-year, suddenly recalls that his world is "Phantom Eclipse," an R18 eroge he created. Despite being a mere mob character, he resolves to enroll in First Soul Wing Academy, the game's setting, primarily to see his favorite character, the high-ranking angel Michael, and observe the story from a distance. After successfully passing the entrance exams, Yuma moves to First Heavenly Demon City.
During spring break, Yuma, eager for a "sacred site pilgrimage," ventures out at night, despite the danger posed by monsters called Kyoju. He stumbles upon the exact alley where the game's prologue event occurs. To his shock, the two main heroines, Seraph (an angel) and Luminous (a demon), fall from the sky. Instinctively, Yuma catches them, injuring his leg in the process. Despite the pain, he's ecstatic to be in physical contact with his beloved characters.
However, their reunion is cut short by the appearance of a menacing Kyoju, a monster born from negative human emotions. Seraph and Luminous, lower-class angels and demons whose wings are degraded and cannot fly, were being pursued. They explain that only humans contracted with angels or demons can fight Kyoju. Yuma, realizing his presence as an "irregularity" might have broken the story's protection for the heroines, feels responsible. He offers to be a decoy so they can escape, but Luminous fiercely refuses to abandon him.
Knowing the game's lore, Yuma suggests a contract, which would grant him power to fight. Seraph and Luminous initially dismiss this, stating they are too low-ranked to form a contract. However, Yuma remembers a hidden game mechanic: angel and demon power can be temporarily amplified by strong emotions. As the Kyoju closes in, and Seraph prepares to sacrifice herself as a decoy, Yuma grabs her hand. He proposes trying the contract, then, with a heartfelt declaration to "definitely protect you both," he triggers their emotions.
In a shocking turn, Yuma contracts with both Seraph and Luminous simultaneously, gaining immense power. He realizes this is due to a forgotten developer's note: a human with two souls (like a transmigrator) could form dual contracts. Enraged by the Kyoju threatening his favorite characters and "distorting" his beloved story, Yuma unleashes his newfound power, defeating the monster with a single punch. He collapses from exhaustion as another heroine, Kirisaki Mizuki, arrives.
Yuma awakens days later in the Michael Union, the strongest angel faction's headquarters, having been healed by recovery magic. He's relieved to have avoided further interaction with Kirisaki, still clinging to his desire to remain a mob. However, his dual contract is an unprecedented event. He's summoned to meet Michael, the benevolent but stern leader of the angel faction, and Lucifer, the powerful and ruthless leader of the demon faction (Luminous's superior). They question how he, a human, could contract with two lower-class beings, especially from opposing factions. Facing the possibility of Seraph and Luminous being "disposed of" or "dissected" due to the anomaly, Yuma reluctantly reveals his secret: he is a transmigrator, possessing two souls, which he believes enabled the dual contract. His revelation leaves Michael and Lucifer in stunned silence, their expressions hardening as the chapter concludes, thrusting Yuma into the very heart of the story he had hoped to merely observe.