Monster in the Lethe? was a Challenge Event in Final Fantasy Record Keeper. The event was set on the Lethe River and allowed the player to recruit Terra to the party.
Faced with the threat of being hunted by the Gestahlian Empire, the Returners and their leader, Banon, must make a bold escape from their hideout in the Sabre Mountains via the nearby Lethe River. Terra and Banon must be protected at any cost.