"Eighty-Six"... It is a derogatory term for people of color who used to live in the Republic of San Magnolia.
They were stripped of their human rights simply because they were colored, forced into battle to fight mechanical weapons called the Legion developed by other countries, and died inhumanely...
The survivor of that war, Shin, moves to the neighboring Federation of Giad and fights the Legion in this war action story!
Why did he choose to fight again after escaping the oppression of the Republic?!