Fall of the Scarlet Ammo (堕ちた緋弾（スカーレット） Ochida Sukaretto?) is the fourth volume of the Hidan no Aria novel series released on August 25, 2009. This volume contains start of the IU arc.
- 1st Ammo - Invisible Bullet
- 2nd Ammo - Emergency Mission -Quest Boost-
- 3rd Ammo - Summer Festival
- 4th Ammo - Infighting -Falling Out-
- 5th Ammo - Golden Pavillion -Abu Simbel-
- Last Ammo - Awakening of the Scarlet Ammo
- Epilogue - Go For the Next!!