Ep. 1: Keita Aono falls into Bottom World and teams with Hinoki Sai in a giant robot.

1

High school student Keita Aono avoids punishment by arriving early, only to spot new student Hinoki Sai, whom he recognizes from a dream and as a childhood friend. After failing to speak with her due to a crowd and her subsequent departure in an Akamatsu Industries vehicle, Keita’s misfortune worsens. He crashes his scooter in the rain, falling into the underground amusement park Bottom World. The park’s opening is delayed following the deaths of 200 workers that day, and Keita’s clumsiness threatens his life as monsters pursue him deeper inside. Just as hope fades, he encounters a giant robot piloted by Hinoki. He joins her as co-pilot, and together they battle numerous enemies until their fuel runs out before their most terrifying confrontation.