Battleground Workers

Jinichirou Taira, an unemployed 30-year-old, suddenly receives a letter telling him to fight against an unknown life form. He is now forced to accept this new job where he has to pilot a new mechanical armor called "RIZE." The name "RIZE" was used because they are the only ones that can hope to save humanity. At the frontline of the battlefield, he is now fated to save the world without anyone ever knowing...!? (Source: Shogakukan, translated)