Bokurano

During a summer camp, 15 children, 8 boys and 7 girls, come across a grotto by the sea. Deep inside, they find working computers and some electronic equipment, and later the owner, a man named Kokopelli. Kokopelli says he is a programmer working on a brand new game, in which a large robot has to defend the Earth against fifteen alien invasions. He persuades the children to test the game and sign a contract. All but one of them sign; barely a moment later, they mysteriously wake up on the shore, believing what happened was just a dream.