The "Sekai (World)" has been under attacks by aliens. One day, Arikawa, one of the staff of the provisional headquarters for the invading aliens, finds a high school boy Kakashi, who is lying on a hill with his memory lost. Kakashi is found to have a power to beat the aliens and starts living together with Arikawa and his boss Shiro. Kakashi gradually gets used to the strange life but the relationship among the three breaks up when Kakashi loses his motivation to fight with the aliens.