I FUCKING LOVE THIS SONG!!!!!
Kawada Mami songs are always awesome and this is no exception, she really makes Shakugan no Shana OPs awesome and the one for the OVA is proably one of her better works so far.
My Shakugan no Shana OP list (updated):
Hishoku no Sora Joint Prophecy Being BLAZE
Here is the PV of the song
You can find Direct Downloads for this song over at Baka-Wolf.com