The civilization of the past, now called Old World, has produced many Relics with its advanced technology. Many rubble of unknown material, high-rise buildings floating in the air, strange medications and a group of weapons that are too powerful to be used by people. After the collapse of science and civilization, people gathered these Relics, and over time they were rebuilding human society. In this way the Hunters were created, the warriors who face the various dangers of the Old World. Akira, a new hunter boy who wants to go up from the slums, entering the ruins of the Old World he meets a mysterious girl who can only be seen by him as a ghost, in a world where hunters are trying to overcome the legacy of the old civilization.