Bokurano

A group of 15 children, 8 boys and 7 girls, attend a summer camp and stumble upon a grotto near the sea. Inside, they find functioning computers and electronic devices. They later meet the owner, a man named Kokopelli, who identifies himself as a programmer developing a new game involving a giant robot defending Earth from alien attacks. He convinces the children to test the game by signing a contract. All but one child agrees. Shortly after, they wake up on the shore, convinced the previous events were only a dream.