In the manga's story, Japan has yet to become one unified country. A sudden cease-fire prevails in the fighting between the Yamato Imperial Court and the native Emishi people over Japan's northeastern Tohoku region. An Imperial Court envoy visits Aterui, the chief of a great Emishi tribe. The envoy who calls himself Sanekage proclaims, "Let's go on a journey to hunt a demon together."

A demon created by a shōmoji entertainer in the Imperial Court had suddenly started attacking people indiscriminately. Aterui had no reason to lend a hand to his careless enemies, but he decides to embark on this journey due to Sanekage's offer related to revenge for Aterui's wife.

The second part of the project is Shōtarō Teshirogi's Kou-Tetsujo Iron Castle novel, which shipped on March 18. Ohtagaki provided the original designs, and Shogakukan's Gagaga Bunko label published the novel.