Somewhere on the continent of Fandell, there is a kingdom known as Wineslem. For hundreds of years, this kingdom has been enjoying a peaceful life. Its inhabitants make wine from the country's fine grapes, and merchants from all over the world travel there. But the era of piece has come to an end. An evil force that was asleep for thousand years has awakened. Ferocious monsters and terrible disease plague the kingdom. One day, a Wineslem girl named Elphie finds an unconscious young man on the lake shore. He doesn't remember anything about his past. But with his outstanding skills, he might become the savior people are waiting for.

Aiza is an action RPG, somewhat similar in layout to Ys games. However, the combat requires the player to actively press the "attack" key (unlike the "bumping" combat in Ys). Defeated monsters bring experience points, which contribute to the hero's automatic leveling up. Beside physical attacks, the hero can also execute special techniques which require "psyche" points.