From the ppn wiki: "In 2005, Utada was listed as the person who pays the most tax in Japan. This is the equivalent in Japan of the 'rich list' (as the amount of tax payed is roughly equivalent to the amount of money made) Star's actual incomes are kept secret, which is why the amount of taxes payed is used."
http://wiki.theppn.org/Utada_Hikaru#Other_Facts