Having surrendered Mazinger Z to Baron Ashura, Kouji is handcuffed and locked in a cell in Undersea Fortress Saluud. Boss, Nuke and Mucha on the other hand, managed to avoid detection by hiding in the Pilder. They break out, defeat several guards and then disguise themselves using their uniform to rescue Kouji and Sayaka. After freeing Kouji however, the Saluud comes under attack from Count Brocken and begins to sink. Eventually, Boss and Kouji rescue Sayaka and make it back to the Pilder and Mazinger...