In April 1945, Koji Namiki boards a submarine on a top secret mission. Inside the vessel, rocked by depth charges from enemy ships, Namiki along with others who have volunteered for the mission, wait impatiently for the submarine's commander to order an attack. Watching them intently is a mechanic, Ito, who greatly admired Namiki when he was a star high school pitcher at the national baseball championships. And, indeed, Namiki has with him a souvenir baseball from those heady days. He grasps it tightly as he awaits the next depth charge. The submarine manages to evade the enemy ships but it doesn't emerge unscathed. One of the four "special weapons" indispensable to their mission has been damaged. Too late. The mission must proceed. Namiki grabs his baseball once again.