Nightmare formed in January 2000 when Sakito and Hitsugi decided to start a band while still in high school. The rest of the lineup came together pretty quickly—Sakito brought in Yomi, Hitsugi recruited Ni-ya, and Zannin joined after hearing his classmates were actually doing this. All of them drew influence from either X Japan or Luna Sea, which basically shaped the whole vibe from day one.

Their sound is built on heavy metal foundations with thick bass lines, unconventional rhythms, and key changes that keep things unpredictable. Though their more recent work, especially the anima album, leans into avant-garde and alternative territory, they've never really abandoned what made them work in their indie days. Over the years they've dabbled in jazz, ambience, electronica, techno, and even bossa nova influences, which shows up in everything from sprawling experimental tracks to surprisingly effective rock ballads. Even when they're going fast and heavy, there's variety in how they approach songwriting.