Nightmare (????? ,Naitomea?) is an influential visual kei band from Japan. They enjoyed mainstream success with the inclusion of "The World" in the anime series Death Note and were considered a major influence in the ongoing visual kei scene.
The World Ruler is Nightmare's fourth full length studio album. In this album, experimentation in styles of electronica, ambience, and usage of live brass are present. Three different versions of this album was released: One with just the CD, one with a CD+DVD, and one with a CD+DVD and a photo book. The tracks "The World" and "Alumina" were featured in the anime Death Note as the first opening and ending songs respectively.