Shinpei Ajiro, a 17-year-old orphan raised by the Kofune family following his parents’ death, shares a deep bond with foster sisters Ushio and Mio. After returning to his isolated hometown of Hitogashima for Ushio’s funeral, he is thrust into a hidden war against Shadows—superhuman entities that replicate and assassinate their targets. His analytical intellect and emotionally detached demeanor, honed by childhood loss, prove vital in dissecting the island’s mysteries. A heterochromatic right eye, later revealed as a relic of the deity Hiruko, unwittingly grants Shinpei the power to loop time upon dying, preserving his memories across each cycle. These resets begin at fixed moments but incrementally advance toward an inevitable cutoff, racing against his efforts. The eye also offers fleeting glimpses of parallel timelines and near-future events, though overexposure risks physical collapse and mental fragmentation. As timelines repeat, Shinpei methodically investigates Ushio’s death, forging alliances with hunter Ginjiro Nezu and researcher Hizuru Minakata. He employs firearms, improvised tools, and recorded evidence to expose Shadows, identifying imposters through subtle discrepancies like mismatched clothing. Navigating betrayals—including those by a Shadow-duplicated Mio—he uncovers Hiruko’s plot to resurrect itself via human sacrifice during the summer festival. Confronting the cycle’s grim mechanics, Shinpei sacrifices himself repeatedly, instructing Hizuru to kill him and reset events. His resolve is tested further by Ushio’s sentient Shadow, which mirrors her personality yet obscures its loyalties, offering cryptic warnings about his powers’ constraints. In final loops, he infiltrates the Shadows’ dimension, synthesizing fragmented insights from multiple timelines to dismantle Hiruko’s network. The climax hinges on his strategic deployment of the eye’s capabilities, balancing precognition, temporal leaps, and parallel-world observations to sever the loop permanently.