Kizuku Oyama commands the experimental submarine SS-99, designed by Dr. Juzou Oki to combat the Ocean Empire's domination of Earth's seas. Appointed by Japan's national defense forces, he leads the vessel and its crew on missions against this oceanic threat. His leadership is just, balanced, and strategically adept. He demonstrates calm decision-making during combat operations, including engagements at extreme depths like 39,600 feet. As captain, he oversees crew operations involving Susumu Oki (chief mechanic), Miyuki Moriki (communications officer), and Torakichi Tanuki (deputy captain). His narrative role centers exclusively on military leadership in the conflict against the Ocean Empire, led by Hell Deathbird.