Shakugan no Shana X Eternal Song - Harukanaru Uta

Set in the 16th century in Europe, this is a prequel story of Shakugan no Shana. In the world where the seals didn’t exist, the Great War burst between the Flame Hazes and the Crimson Denizens. The story centers around Mathilde Saint-Omer, the former “Flame-Haired Burning-Eyed Hunter” and reveals details that haven’t been explained in Shakugan no Shana.