Natsu dayo!!

 is the eighth single by X21.

CD Only CD

 * 1) Natsu dayo!! (夏だよ!!)
 * 2) Egao no Prologue (笑顔のプロローグ)
 * 3) Zettai Heroine (絶対ヒロイン)
 * 4) Natsu dayo!! (夏だよ!!) (Instrumental)
 * 5) Egao no Prologue (笑顔のプロローグ) (Instrumental)
 * 6) Zettai Heroine (絶対ヒロイン) (Instrumental)

CD+DVD CD

 * 1) Natsu dayo!! (夏だよ!!)
 * 2) Egao no Prologue (笑顔のプロローグ)
 * 3) Natsu dayo!! (夏だよ!!) (Instrumental)
 * 4) Egao no Prologue (笑顔のプロローグ) (Instrumental)

DVD

 * 1) Natsu dayo!! (MUSIC VIDEO)
 * 2) Natsu dayo!! (MUSIC VIDEO Off-shot)

Trivia

 * Costumes for the title track were produced by Fujita Nicole.