I agree about the Madonna comparison, but too many times Ayu is compared to Britney, and they have nothing in common. Not music, style, personality or anything. The popularity maybe yeah, but I think Ayu's popularity in Japan is more like Madonna's.
I'd compare Koda Kumi to Rihanna, maybe? Only with Kuu having a better voice. But their music style is similar, and their styles have a lot in common too. Though I don't like Rihanna that much.
