"Niji" (虹, "Rainbow") is the eighth single by L'Arc-en-Ciel, released on October 17, 1997 it reached number 3 on the Oricon chart. It also was their first release after sakura's arrest and the debut of yukihiro as the band's support drummer (he officially joined on January 1, 1998). The title track was used as the opening theme of the Rurouni Kenshin movie Ishin Shishi e no Requiem. Making them the only artist to contribute more than one song for the franchise. The single was re-released on August 30, 2006. The song is one of the band's signature songs, often played when closing out concerts.
American R&B group TLC recorded an English-language cover, titled "Rainbow", for L'Arc~en~Ciel's 2012 tribute album. Female heavy metal band Show-Ya released a version of the song on their 2014 cover album Glamorous Show ~ Japanese Legendary Rock Covers.