In the mid-20th century, as a result of the economic crisis and a collapsing birthrate, Japan was on the verge of becoming a failed state.

By the year 2061, the Boundary War has ended but Japan has been divided into four occupied zones where native Japanese are treated like second-class citizens.

[9][2] An original net animation spinoff series titled Amaim Warrior at the Borderline: UltraSteel Ogre-Gear (Japanese: 境界戦機 極鋼ノ装鬼, Hepburn: Kyōkai Senki Kyokkō no Sōki) is also produced by Sunrise Beyond and will premiere in Bandai Spirits' YouTube Channel on April 10, 2023.

[13] Masami Obari will direct the series alongside returning staff from the previous anime handling the writing (Noboru Kimura), music (Rasmus Faber) and mecha designs (Ippei Gyōbu, Kanetake Ebikawa, and Takayuki Yanase).

[16] Chinese streaming website Bilibili removed the series from its service due to the portrayal of Asian foreign powers as human traffickers in the fifth episode, "Determination".