It's the emotions in her voice... I shall use the songs kendelle said to illustrate an example. Ayu sang NEXT LEVEL, Sparkle and Days all in the same album, yet her voice in each of these songs is so different, and each carries a different emotion, and it corresponds to the song's real Emotion as well.
She can be lalala-ing, but even that would have feelings too. It's just special... just like this.
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YAYAYAYA GAGAGAGA DADADADA WOWOWOWO
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