The year is 2084 and the world has changed. Wracked by calamities and crawling with monsters, the last remaining humans face a dangerous existence.

And now, the Earth has been sent a message from the deepest reaches of space - a dark countdown to the extinction of all humanity. But there is hope! Five thousand children will be rescued by these mysterious message-senders.

This is the journey of Hototo, one of the lucky five thousand - but only if his teenage sister, Tala, can safely deliver him to the nearest Beacon before time runs out.