Rungo Iron is a large, physically imposing fighter known for immense strength and skill with heavy weaponry, typically wielding massive blades or blunt instruments. Originally a soldier, the abrupt end of a war left him purposeless, driving him into mercenary work. He was contracted by a powerful secret organization to compete in a high-stakes fighting tournament, battling opponents at their command.

He later uncovered their criminal operations. This discovery shifted his focus beyond payment towards seeking redemption and opposing the organization. He allied with Eiji Shinjo, a fellow fighter sharing the goal of dismantling the syndicate. Together they entered subsequent tournaments and conflicts engineered by the group, actively targeting its leadership.

After the primary antagonists' apparent defeat, Rungo adopted a nomadic life. Fighting ceased to be for profit; he now followed a self-imposed duty to combat injustice and protect others. He intervened in new conflicts where innocent lives faced threats from emerging malevolent forces, opposing evil wherever he found it.

Years later, Rungo encountered a young fighter named Subaru. Recognizing Subaru's potential and shared need for guidance against dark influences, Rungo took him under his wing. Traveling together, Rungo provided training and support, helping Subaru navigate the fighting world's dangers and confront personal challenges. This mentorship reinforced Rungo's commitment to using his strength protectively.