Daisaku Sakaki is a pilot in the World War II-era Kishin Corps, operating the amphibious combat robot Ryujin (later renamed Kishin Dragon). This blue mecha excels in aquatic environments, achieving a swimming speed of 25 knots and transforming into a submarine. Its armaments include two 53cm torpedoes mounted on its back and a pair of 7.7mm machine guns housed in the head. Technically, the Ryujin weighs 36 tons, walks on land at 29 kilometers per hour, and carries a 1,200-liter main fuel tank. Sakaki conducts missions transported across the Pacific Ocean aboard a large, unnamed submarine specifically designed for Ryujin deployment. His combat operations with the Kishin Corps contribute to the global war effort against alien invaders.