Sparkle isn't a dark song at all.
Sometimes I think people expect a PV where she's in a club dancing ****ty and wooing guys and shoving them off. That's the typical PV for this song, and as much as I'd like to see Ayu doing that (
) I know she has more depth than that to her song. It's a bit of a "**** you" since so many have said the lyrics are not 'deep'..