The 2500 series is made up of re-releases of old Sega games, though the exact nature of each release varies somewhat. Some games (such as Vol. 16: Virtua Fighter 2) are mostly straight ports of the originals, while others (such as Vol. 1: Phantasy Star Generation 1) feature updated graphics, updated audio and changes to gameplay. Other releases fall somewhere in between. The games in the series are released only for the PlayStation 2, and only in Japan.