 Earth's only hope is the submarine called "Super 99", a mysterious submarine designed by Dr. Juzou Oki.The story begins as Japanese forces decided to investigate the mysterious threat beneath the ocean.Goro Oki gives his younger brother, Susumu, a rifle, a weapon modified from Type 99 rifle of the World War II era; Susumu is also given a key bearing a "99" marck by his grandfather Juzou.