Ruupu/Loop is one of my all-time favorite songs! I heard it as the ending song to Tsubasa Chronicles and have it on my iPod! It's the first song I memorized completely of Maaya Sakamoto's.
I love this song. Since it's the end theme to Tsubasa Chronicles (2nd ending) I've loved this song since I first watched that series. Now it's on my iPod and I listen to it so often!