"Fighter" is set in Japan in the near future. In 2061 AD, Japan is occupied and ruled by other countries. The world is divided into four major economic circles, and the Japanese, as subordinate citizens, are oppressed every day. The 16-year-old boy Shiiba AMOU is not good at socializing and lives a gloomy life every day. However, an encounter with the self-disciplined AI "GAI" one day not only changed him, but will ultimately change the fate of Japan.