Senior Private Tokimune Susumu is a young and reckless soldier of the Arandas Army's 8th Autonomous Unit assigned to pilot a Trail Krieger. He has a strong sense of justice but lacks experience.

Because of his idealistic attitude, he repeatedly violates orders much to the chagrin of his fellow soldiers. In one certain occasion, he disobeyed instructions and saved a civilian trailer being tailed by Ingelmian troops. The said trailer contained the titular mecha, Argevollen, which he used in his first battle without knowing that he became its exclusive pilot. Lieutenant Samonji would later put him in charge of the mecha.