Arata naru Sekai: Kako-hen

A group of individuals traveled from a distant future where most adults have mysteriously vanished, leaving children under the care of a small number of remaining adults. Their stated goal is to uncover the reason behind the human population's decline and prevent it from occurring. A boy in a movie theater seat messages on his phone, questioning whether five children can realistically alter the future without proper planning. He and others are uncertain if they have actually traveled to the past, as they have not left the theater since arriving.