Shakugan No Shana

Shakugan No Shana is a Japanese anime series with three seasons, all containing 24 episodes. It aired between October 6, 2005 and March 23, 2006. Two OVA's and three movies were also released.

Plot
Shakugan No Shana details an age-old conflict between those who inhabit the Crimson Realm, a parallel universe to the human world. The Crimson Realm is populated by Crimson Denizens, who are able to manipulate the Power of Existence, a fundamental power within any biological entity and functions as "fuel" for one's existence. Denizens whose power stands out among their peers are known as Lords of the Crimson Realm and Lords that are even more powerful are known as Gods.

Denizens who do not care about the balance between the Crimson Realm and the human world collect Power of Existence from humans to use for their own purposes. Some Lords contract with humans to become a Flame Haze, whose duty is to maintain the two worlds' balance by destroying any Denizens disrupting it.

The story largely takes place in Misaki City in Japan and begins when high school student Yuji Sakai is thrown into the middle of this conflict and encounters a Flame Haze girl with flaming red eyes and hair dressed in all black wielding a katana. The girl informs him that he died some time ago, and that he is a Torch, a human with greatly diminished Power of Existence, and whose remaining Po

wer of Existence will slowly run out. In addition, Yuji is a special kind of Torch who can move within Seals known as a Mystes, who contains a Treasure Tool, a magical object created by Denizens that can provide special abilities or even Powers of Unrestraint. Unfazed by his apparent death, Yuji befriends the girl and names her "Shana" after her sword. They later discover that the Treasure Tool within Yuji is the Reiji Maigo, which restores his Power of Existence every night at midnight.

Trivia

 * In the Funimation dub, Shana is voiced by Cherami Leigh, who voiced anotherTsundere literal Fiery Redhead with a sword in  Kaze no Stigma.