I always thought Namie's career and music reminded me a bit of Mariah's. They both started off with more pop stuff and had quite an innocent image, but they later got more and more heavily into hip-hop (though Mariah moreso) and also have done some suggestive songs in the past. They're also older ladies who still look better than girls 10 years younger than them.
Although they aren't completely similar, as Mariah has the huge voice and Namie's got the dance moves.
I think the most difficult person to compare would be Hikki. When she was first introduced in America a lot of people called her Japan's Britney Spears, but I definitely do not think that is an accurate label

. Can you imagine Britney doing "Passion"?