Zill O'll (ジルオール) is a 3D role-playing video game and one of Koei's most successful IPs for the genre. The game's appeal over other titles of its time is its free-scenario system. The game's title is an acronym for "Zillion of Wills". It hasn't been localized, although its action-RPG prequel has been shipped overseas. The PSP re-release Zill O'll infinite plus includes several additions to differentiate itself from the original title.