Epic necro bump, but while wandering the sea of interweb, I ran into this: http://www.nicovideo.jp/watch/sm3891722
Title is Hatenaki Sora, Hateru Sekai. It was made by Hull, the same person who created EXEC_RESOLUTION/. and, while the lyrics is Japanese only, the video does have some bits of Hymmnos font.
A remake of this song was included in Hull's newest CD, 忘郷少女とアストロラーベ (just released very recently during C81, Dec 2011).