In the town of Orth, orphan cave raider Riko dreams of descending the Abyss, the immense pit at the world's center, to find her missing mother. After she rescues a boy with a robotic body whom she names Reg, the two set out together into the depths, where the curse of the Abyss inflicts worse sickness on anyone who tries to climb back up. This first compilation film condenses the opening half of the TV season and serves as a recap rather than a standalone entry point.