The composition in this piece is not bad. I like the creativity with the text, after all, vocaloid is centered around the theme of music. The contrast can be better I suggests you do more of it.

Blurring the BG works in creating some depth in some sigs but not all the time. In most cases, because people misuse it, it causes the entire compo to seem a bit LQ. You don't want that. In this case, I see some LQ to be truthful. The focal seems LQ IMO. I would have left the darker area blurred but the area past the focal where the colour is more visible sharpened. It would show a nice transition between the compo and colours.

Its a nice piece still Nice work.