Hello everyone,
Here we are for another character focus corner (the second till now).
Let's cover another of the most famous character out there, I'm talking about Shana of the light novel/manga/anime series Shakugan No Shana (that is planned to have a third season adaptation soon)
Shana (nickname given to her by the protagonist Yuuji Sakai) formerly known as "Enpatsu Shakugan no Uchite" is a rather ancient woman (no precise date is given as her birth date, but as Flame Haze do not age after being contracted it's a little difficult to figure out) into a body of a little girl of an age around 14-15 (speculation as we don't really know)
Her personality is a tsundere trying to find her way to express feelings she for a long time don't even know she had. (And Yuuji is expert at failing to notice this, even if it seems that in the novel he finally noticed so there is hope for a third season!)
She is shown as incredibly intelligent and taking maximum votes in each school test. (Probably old knowledge as she said that was not the first time she faked to be a schoolgirl in her flame haze life)
Her powers are flame manipulation based (with Alastor is her partner it is somewhat obvious), but she prefer mostly to use her sword to hack and slash her own enemies. She is capable of growing flame wings to fly for a short while and is shown capable of controlling power of existance (at least in the anime).
While she is powerful and intelligent she is found to be rather naive to social affairs, she has been capable of asking "where babies comes from" and that is a rather impressive feat for someone who lived for centuries. 
Shana is also the character who showed most growth in this series, starting as an apathic character avoiding social contact and becoming slowly a rather passionate, happy and playful schoolgirl even culminating in falling in love with Yuuji.
She has a particular antic that makes her easily recognizable. If someone irritate her, she starts screaming "urusai urusai urusai" in rage!
Concluding, she is a rather enjoyable character, you'll end up loving as soon as you get to know her better. She is also voiced by Kugimiya Rie so what can go wrong now? 
See you soon,
feal87