Hiroshi and Mayumi grew up together. They went to the same kindergarten, the same school, always spent time together, and naturally thought that they will never separate. Then the time has come when they both had to go to different colleges. They promised each other than they will still be together. But they both broke the promise... If jealousy and the knowledge of one's own betrayal were not enough to endanger their relationship, something far worse happened... the man with whom Mayumi spent the night was found murdered, and Hiroshi must forget his personal pain in order to solve the mystery... Pias is a traditional Japanese-style adventure. The gameplay consists of choosing verb commands ("Look", "Talk", "Ask", "Think", "Move") from a menu. Typically, events are triggered by depleting all the commands at every screen. The game has scenes with explicit sexual content.