Shuichi Kagaya, a reserved yet sharp-minded high school student yearning for an ordinary life, finds himself thrust into a surreal existence where he can morph into a monstrous, dog-like mascot costume marked by a spine zipper. This transformation unlocks heightened physical prowess—superhuman strength, agility, endurance, and an acute sense of smell lingering even in his human state. The costume’s hollow interior permits others to inhabit and control his body, their synergy and aligned objectives magnifying their collective power. During intense stress or a fervent urge to shield his host, this alliance can fuse their bodies and memories into a singular being, unlocking advanced capabilities like manifesting weapons—katanas, dual pistols, or others shaped by his partner’s traits. His past conceals a fractured romance with Elena Aoki, who erased not only their shared history but also memories of his childhood companions. Her alterations extended to his parents, whom he long assumed were merely absent due to work—a lie unraveled upon discovering their erasure by the entity Honoka. These deceptions feed his inner turmoil and growing alienation from humanity. Initially repelled by his monstrous form, Shuichi hardens into a detached, self-sacrificing protector after rescuing Clair Aoki from a suicide attempt. Clair’s relentless crusade to expose her sister Elena and avenge their parents’ deaths drags him into morally fraught battles, culminating in lethal violence against a vengeful gang member—a line he once refused to cross. An extraterrestrial known as the Alien, distributor of power-granting coins, reveals Shuichi’s monstrous guise mirrors his inner void and craving for others to “fill” him, entwining him in a codependent bond with Clair. Their alliance evolves from wary coexistence to profound emotional reliance, her ruthlessness compelling him to harness his abilities even as his self-esteem fractures. Physical scars, like the neck wound from Elena decapitating his transformed body, become emblems of his trauma and tenacity, marking his capacity to survive injuries fatal in human form. Fusion events gradually mend his splintered memories, unearthing suppressed truths about Elena’s machinations and their shared past. These discoveries, paired with clashes against other empowered individuals, spur his quest to unravel the origins of his powers—a pursuit demanding steep personal sacrifices, yet forging a path toward reclaiming his fractured identity.