Bokurano

the long version

During summer vacation a group of fifteen children discover a mysterious man living in a cave Surrounded by high tech gadgets, the man claims to be a game developer, creating a video game with a giant robot defending Earth from fifteen alien invaders. He asked the children to test the game for him and they happily agreed. The fun soon turned to horror, the first child to play died shortly after winning. Worse still they had no idea how to end the game.