Shin Megami Tensei: Digital Devil Saga, known in Japan as Digital Devil Saga: Avatar Tuner, is a duology of PlayStation 2 role-playing video games developed by Atlus. It is a spin-off of the Shin Megami Tensei series of video games; the story focuses on specific characters who become demons and have to consume their own to win a war and reach the "Nirvana". The first game was released in Japan on July 15, 2004. The story to Digital Devil Saga is continued with its direct sequel Shin Megami Tensei: Digital Devil Saga 2, known in Japan as Digital Devil Saga: Avatar Tuner 2 where the returning characters find themselves in a postapocalyptic world. Notable features of the games include the ability to shapeshift between demon and human forms in battle, and a return of the "press turn" battle system from Shin Megami Tensei: Nocturne. A large difference between Nocturne and Digital Devil Saga is the ability to change equipped skills at will, instead of at level up. Unlike in Nocturne, unlearned skills are not lost forever, which allows for much greater character customization.