Kaijin

Originally a dwarf from the nation of Dwargon and born a commoner, he was a famous blacksmith in human countries but originally a researcher. He once served as the captain of the royal palace knights' engineering corps. When Rimuru visited Dwargon in Volume 1 (Episode 4 in the anime), he formed a connection and moved to Rimuru's side after a dispute with Vester, bringing along his childhood friends, the three brothers Garm, Dold, and Mild. After moving to the Jura Tempest Federation, Kaijin was in charge of forging weapons, Garm handled clothing production, Dold was responsible for tool production, and Mild took on construction, arts, and urban planning, playing a crucial role in enhancing the federation's technological capabilities and the value of its products.

In Volume 2, Kaijin delegated the production of weapons to Kurobe to focus on managing production and research. In Volume 3, he reconciled with Vester, who had also taken refuge in the Jura Tempest Federation, and the two collaborated on developing the Spirit Magic Core. In Volume 7, he and Mild traveled to the site of a new city in Milim's territory to oversee its construction.