Shuuichi Kagaya appears to be an ordinary high school student, yet he harbors a monstrous secret within him. Unable to comprehend the origins of his powers, he endeavors to keep this side of him concealed from the world. When he rescues a girl named Claire Aoki from a burning building one fateful night, his hidden identity is exposed. Claire, determined to unravel the mystery behind Shuuichi's transformations, resorts to extreme measures, pushing him off the school roof. Forced to reveal his monstrous form to save himself, Shuuichi becomes entangled in Claire's quest to locate her own monster-affected sibling. Together, they embark on a journey filled with peril and revelations, all while being pursued by others with a vested interest in the truth.