Ai City

In the future, Kei and Ai run for their lives, Ai is a small girl she holds a deep secret that can destroy the world. The world is populated by Headmeters people that have psychic powers and strong strength. When Headmeters fight their strength is shown on their forehead but Kei's for some reason never went beyond level five but other Headmeters's strength has. Kei has the ability to increase his strength when Ai gets in trouble.