[3][4] Gai is a young man who is an apprentice to the blacksmith Amon, who found him as a newborn with the legendary cursed katana Shiryū, which drove his mother to commit suicide rather than be consumed by its bloodlust.

Shiryū is revealed to be one of many cursed weapons that turn their wielder, who is known as a Chrysalis, into a thrall who embodies their murderous impulses.

Over time, a Chrysalis gradually loses their humanity until they transform into armored monsters called Busoma.

An anime adaptation originally developed by DLE and Fields was scheduled to air in April 2016,[7] but it was delayed indefinitely until Netflix streamed the series worldwide on March 23, 2018.

[8][9] Tomohito Naka directed the series while Takahiro Ikezoe served as the chief director, Inoue himself wrote the scripts, Atsuko Nakajima designed the characters, Toshiki Kameyama was the sound designer, and Kotaro Nakagawa composed the music.