From Boku-Tachi:

The two planets of Inferia and Celestia are bound together by the 'Orbus Barrier' to make Eternia. A young girl, Meredy, from Celestia is sent to Inferia to gain the help from the Inferia summoning elements, 'The Greater Craymels'. Their purpose is to aid the prevention of a crash-course collision of the two worlds, known by the denizens of both worlds as the 'Grand Fall'. Upon landing in Inferia, she joins the entourage of 3 young villagers named Rid, Farah, and Keel in her journey. Based on the game Tales of Eternia by Namco.