It is the 13th century, and the flames of war have engulfed East Asia, with Genghis Khan poised to conquer the world. In the Mongol Empire's latest campaign, the Tangut people become the target. Following the recent defeat of Shut Hell—a notoriously vicious female Tangut warrior—the invasion is expected to be swift and effortless. However, this conquest differs from others; the goal is not merely to seize the land, but to utterly destroy Tangut culture and erase them entirely from history. In present-day Japan, Sudou is a high school slacker plagued by vivid dreams of ancient times. One day, he meets a sullen transfer student named Suzuki, who shows an odd interest in him. However, their encounter is set to drastically alter his life. When Suzuki cries out "Shut Hell," Sudou finds his world slowly fading to black. Awakening at an abandoned gallows, Sudou finds himself centuries in the past, now inhabiting Shut Hell's body. He is soon discovered by Yurul, a young boy who resembles Suzuki and possesses a complex relationship to both the Mongols and Shut Hell. Realizing that "she" remembers nothing, Yurul begins to recount the tale of how they met and their current situation—one that makes them the target of the world's most ferocious empire.