Keita Aono is an average high school student who enjoys discussing military technology and the girls in his class with his friends. One day, he is surprised and delighted by the arrival of a new transfer student, his childhood friend Hinoki Sai. However, when Keita attempts to catch up with Hinoki after school, he accidentally stumbles into Bottom World—an underground amusement park whose opening was canceled following an unexplained tragedy. As Keita explores the area, he eventually locates Hinoki in the cockpit of a strange robot. She is there on behalf of Akamatsu Industries, a company contracted by the secretive international organization Mode Warp to investigate strange cases of violence worldwide. After joining Hinoki in the robot, the pair attempt to defend themselves against the various attractions of Bottom World, which have come to life and turned violent. However, they are unable to escape until a man with transforming powers—dubbed "Betterman"—joins their struggle. Faced with an enemy he does not understand and a slew of mysterious new technology, Keita joins Akamatsu Industries in a fight against a force they call "Algernon."