In near-future Tokyo, trauma psychologist Hana Mori investigates a mysterious phenomenon where people who experience clinical death return changed—speaking foreign languages or possessing impossible knowledge after claiming to have lived through "a 24th hour" in the day. When graffiti artist Kenta Yoshida becomes the latest victim, suddenly speaking fluent Russian and drawing the same unknown circular room repeatedly, Hana discovers a government conspiracy led by Dr. Furuya. The phenomenon has affected dozens of people, all connected by synchronized brain activity. Hana learns she too experienced this "24th hour" during a childhood drowning incident, explaining her recurring nightmares. The truth emerges: forty years earlier, a temporal physics experiment created a tear in reality—a pocket dimension accessible only at the moment of death.