
Leaving with no choice, the Flame Haze strikes her sword and tears a large gash off Yuji's shoulder, slicing off the enemy's arm in the process. As the Flame Haze is about to deliver the final blow, a confused Yuji goes in the way, and is instead attacked by the enemy. Then, she attacks another creature this time, it is in the form of a woman, and that creature mockingly identifies the girl with blazing-red hair and eyes as the "Flame-haired Burning-eyed Flame Haze of Alastor, 'Flame of Heavens'". The girl with blazing-red eyes soon ask about Yuji's existence, and like the creatures she defeated, a voice she refers to as "Alastor" assumes that he is a Mystes. Soon, she confronts the creatures in front of her and mercilessly defeats the two. As the gigantic baby doll cries in pain, Yuji finds a girl with blazing-red eyes and hair standing in front of him. until a blade slices its arms cleanly off. Curious about his identity, one of the creatures grabbed Yuji and attempted to devour him. The two creatures discover that Yuji can move about in the Fuzetsu, and deducts that he might be a Mystes.

I am pretty sure this is the anime your describing as this takes place in Episode 1 if I am not correct. I believe the anime you may be describing is Shakugan no Shana.
