The story of Riviera: The Promised Land begins a thousand years after the great Ragnarok war, where the gods created Grim Angels to save the world from demons. However, when a rumor of the demons' return spreads, one of the Magi, Hector, orders the Grim Angels Ein and Ledah to activate "Retribution", a power that would eliminate the demons but also destroy Riviera. Ein is defeated by the guardian of Riviera, Ursula, and wakes up with amnesia, unaware of his past and future role in the land.
The gameplay of Riviera: The Promised Land takes place in a unique style where the player cannot physically navigate a character to explore the game world. Instead, players use "triggers" – events that lead to cutscenes, combat, items, etc. by spending special trigger points earned during battles. By investigating areas and moving from screen to screen, players can activate these triggers.
The battle system allows players to select three active combatants out of five, choose a formation for the party (attack- or magic-oriented), and pick which four items to bring into the battle. Items have unique skills that characters can use by filling an "OverDrive" gauge, but they break after being used a limited number of times. Dating gameplay elements are also present, where players make decisions about Ein's relationships with his female companions, affecting one of multiple endings determined by their bond.