Shakugan no Shana X Eternal Song - Harukanaru Uta

Saving the World Is Easier Than Falling In Love Yuji Sakai is beginning what he thinks will be another boring year of school. But everything changes when the world around him stops, the surrounding people are engulfed in blue flames and a freakish doll-like creature begins sucking them up! Before Yuji suffers the same fate, a young redheaded girl with a sword appears and saves him. Yuji is drawn into the struggle between these creatures from another world: the Crimson Denizens and the girl Shana, called Flame Haze. He too has a crucial role to play in the conflict, despite the fact that…he's dead!

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.