Manga by Osamu Kine, Kamen Rider Agito's Toshiki Inoue, Garo's Keita Amemiya launched in 2012

The September issue of Shogakukan's Monthly Hero's Magazine revealed on Tuesday that the planned television anime adaptation of Toshiki Inoue, Osamu Kine, and Keita Amamiya's Sword Gai manga will now premiere on Netflix worldwide simultaneously in spring 2018. In addition, it revealed Inoue will be in charge of series composition and will pen the scripts for the anime.

The magazine did not reveal whether Sword Gai The Animation would be a film, but it did not indicate that it would be a series.

Monthly Hero's Magazine originally announced the anime in 2014. At the time, the announcement noted that the anime will be a collaboration between Flash anime studio DLE Inc. (Eagle Talon, Thermae Romae) and entertainment content company Fields.

The story revolves around Gai, who was born beside a woman who met her death in a forest. He was adopted by the swordsmith Amon. A few years later, Gai becomes Amon's apprentice, and during the forging of a sword, he loses his right arm. To help him, Amon crushes the demon sword Shiryū (lit. Death Dragon) to form it into Gai's replacement right arm. Gai then is able to fuse with the weapon on his arm, and fights against his enemies.

Inoue (Kamen Rider 555, Kamen Rider Agito, Chōjin Sentai Jetman, Chaos;HEAd series composition, screenplay) wrote the manga's story, while Osamu Kine drew the manga from original character designs by Keita Amemiya (Garo creator/director, Zeiram character design). The manga began serializing in the December 2012 issue of Monthly Hero's Magazine , and ended in October 2015. Shogakukan published six volumes for the series. A sequel series, titled Sword Gai Evolve and with the same creative staff, launched in Monthly Hero's Magazine in November 2015, and is currently ongoing. Shogakukan published the manga's third compiled book volume on June 5.

The manga already inspired a 3D CG promotional video by Digital Frontier (Wolf Children production, Summer Wars 3D graphics) in 2013: