Niji no Oto

 is the sixth single by Aoi Eir. It was first released as a digital single before a limited physical edition was released. The song was used as the theme song for Sword Art Online: Extra Edition.

Limited Physical Edition CD

 * 1) Niji no Oto (虹の音)
 * 2) Yume Sekai (ユメセカイ) (Tomatsu Haruka cover)
 * 3) INNOCENCE (Live at Shibuya Koukaidou)
 * 4) Niji no Oto (虹の音) (TV size ver.)
 * 5) Niji no Oto (虹の音) (Instrumental)

Limited Physical Edition DVD

 * 1) Aoi Eir “Special Live 2013 -Starlight Reunion-” 2013.10.28 at Shibuya Koukaidou
 * 2) Avalon Blue (アヴァロン・ブルー)
 * 3) AURORA
 * 4) Sirius (シリウス)
 * 5) Ei! Ei! Ruuuu!!!!!!