Light Novel Volume 0

Light novel volume 0 — a special volume that is included in bru-ray disks of High School DxD HERO. There are events which happened few hundred years prior to light novel volume 1 in it: how Sirzechs and his friends became new satans, how they took part in civil war of Underworld and other.

Chapters

 * Chapter 1. Crimson-haired prince of destruction
 * Chapter 2. Future of devils
 * Chapter 3. Those who surpass the satans
 * Chapter 4. The birth of Sirzechs Lucifer and Rias Gremory

Trivia
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 * At the moment it's the only volume that has official English translation. The translation done by FUNimation Entertainment.