Shakugan no Shana

He had thought his normal days would last forever, until they were ended abruptly by an encounter with a girl with red hair and eyes. He named her Shana.

Not long after he enters high school, Sakai Yuji s normal days come to an end. He sees something bizarre on his way home: people are frozen in a strange fire, and a monster that looks like a large doll is attacking them. Just when he's about to be killed, a girl in a dark cloak wielding a large sword appears, and slices the monster in half. Although Yuji survives the strange encounter, the girl informs him of a desolate truth: " 'You' don't exist anymore."

She calls herself a Flame Haze who hunts "Guze no Tomogara"; intruders from another world. She explains to him that he is a "Torch", a substitute of Yuji whose existence has already been devoured. She also told him that he is a special Torch, "Mystes", which contains a precious item in it. When he looks at his chest, he sees within himself a faint flame, just as she said.

It is in this way that his eternal struggle alongside the girl begins.

(Source: AnimeNfo)