During the great Ragnarok war, the gods of Asgard were overrun by demons from Utgard. In order to save the rest of the world from demons, the gods sacrificed their lives to create Grim Angels, black-winged warriors armed with sacred weapons known as "Diviners". The Grim Angels defeated the demons, and turned Utgard into a beautiful land, Riviera.

Thousand years later, a rumor concerning the demons' return begins to spread. Hector, one of the seven Magi entrusted by the gods to watch over Riviera, sends the Grim Angels Ein and Ledah there, ordering them to activate the "Retribution", a power that would eliminate the demons but also destroy Riviera. Ein is defeated by Ursula, Riviera's guardian, and wakes up with amnesia, unaware of his past and the role he will have to play in the future of the land.

Riviera: The Promised Land is a Japanese-style role-playing game. Unlike most RPGs, it does not allow the player to physically navigate a character to explore the game world. Instead, the player activates "triggers", i.e. events that lead to cutscenes, combat, items, etc., by spending special trigger points earned during battles. This is done by investigating areas, moving from screen to screen.

Once a turn-based battle is triggered, the player selects three active combatants out of the available five, selects a formation for the party (attack- or magic-oriented), and chooses which four items to bring into the battle. The items activate skills for various characters; if a character has been trained with that item, he or she can use powerful "OverSkills" by gradually filling the OverDrive gauge. Items can be used a limited amount of times before they break.

The game also contains dating gameplay elements. The player can make decisions for Ein concerning his female companions, raising or lowering their trust level and eventually reaching one of the multiple endings determined by the relationships between Ein and the young women in his party.