Saotome Institute, which is the center of Getter Ray study, was attacked by a mysterious monster. That figure was a huge "Oni", which is a legendary monster. They fought with a prototype Getter Robo against it. However, they noticed a big fault. Manipulating Getter Robo was a burden to the pilot, and the normal person couldn’t stand it. To provide for the next attack, they had to look for the candidates for the pilots.