Apparently this is the OP theme for a newly aired anime, Ookami Kakushi.
To be honest I’ve never heard of the anime, but while writing this I checked it out and looks pretty good, it’s got that Fate/Stay Night ambience to it, might gonna give it a go =)
Also, for those of you uninformed ones, yes the 2 girls in the video are members of Kalafina, Wakana and Kaori. These awesome (looking) singers are Yuki Kajiura’s solo projects and I guess that means she’s free to mix and match them however she wants eh ? I’m not complaining as long as they keep making awesome songs like this one.
The single is already out so grab it from YesAsia – Toki no Mukou, Maboroshi no Sora!