A few years ago, a massive meteorite crashed into Earth. A mysterious capsule thought to belong to aliens was found inside it. This object, called the "black box," led to the formation of an international organization known as "Project BB" to investigate it.
Eight boys, including Manabu Yoshimura, are students at International Academy, a school situated near Project BB's headquarters. Their teacher, Toukichi Hashiba, lures them with the promise of extra credit, and they end up taking part in his experiment. The plan involves entering the eight empty compartments within the meteorite. Hashiba theorizes that the meteorite reacts strongly to intense human thoughts. He instructs them to vividly imagine a cool, giant robot—if they do, something should happen.
Then, a huge spaceship appears in the sky, and an alien named Wercury shows himself via a 3-D projection. He announces that he comes from the Star of Prokimasi and has arrived to reclaim the meteorite belonging to the Choshin people. If Earth does not hand it over, he will challenge them to a battle. Manabu and his friends are bewildered by this sudden development, but the meteorite responds to their collective thoughts and begins to transform into a giant robot. Attacked by the invading Prokimasi robot, they are forced to unite their efforts and fight back. However, coordinating the wills of eight individuals into one is extremely difficult, and the robot cannot perform as it should. The giant robot, which Hashiba names "Gakusaver," and Manabu's group—can they protect Earth and the meteorite from the Prokimasi invasion?