User blog comment:LittleMixButterfly08/Music for anime shows/@comment-106.67.165.226-20140701111650/@comment-7418318-20140701194605

It's not the metal, tenroujima, slow or piano version and it's certainly not the movie version, so that leaves only the actual main theme. It might be a slightly altered (and unreleased) version of it, but the arrangement is still the same as the main theme.