When the brilliant scientist Dr. Oki vanishes after creating an innovative submarine, his son Susumu suspects a sinister plot by a mysterious faction. Armed with detailed knowledge about his father's cutting-edge creation, the 'Super 99,' including its arsenal, features, and capabilities, Susumu believes that uncovering the truth behind his father's disappearance means exposing the clandestine group known as the Helmet Party and thwarting their malevolent plans. Supported by his allies and the Marine Corps, Susumu embarks on a perilous underwater journey, unaware of the grave risks awaiting him.