Shana is the main heroine of the Shakugan no Shana media franchise.
She is the Flame Haze bound as contractor to the Crimson God Alastor; their job is to stop other Crimson Denizens from running amok. The series begins when she gets involved with Sakai Yuuji, an ordinary high schooler who's been imbued with a powerful artifact that can't fall into the wrong hands. Shana becomes his protector, and gradually more like a partner as he learns to fight; in turn, sharing daily life with Yuuji gradually brings Shana out of her shell (she's always lived in the world of Flame Haze, to the point of not even bothering with a name till Yuuji gives her one).
Shana is often seen wearing a pendant, the vessel of Alastor, and wielding the sword she's named after, the Nietono no Shana. She sports long hair (black normally, red with a flame effect when she's fighting), an ahoge, and zettai ryouiki. Her closest connections are with Alastor (partner and advisor), Yuuji (love interest), Yoshida Kazumi (friend/love rival), and Wilhelmina Carmel (mother figure). Her love for melon bread is the stuff of legend.
(See Shana-tan for the chibi Shana from the DVD extras.)