I like her 5 year old voice, personally. Maybe it's just the paedophile in me. I listened to all the ones you mentioned, and they just sound more like Western singers.
I'll check them out.Asian Kung-Fu Generation: Highly popular by their US fans, but not that special in Japan. They have the sound, and definitely the talent.. but aren't as big as they should be, simply because they don't have "the look". Group of guys who look like your average, in the garage, rock band nerds.
Boom Boom Satellites: Highly talented group that has been around for quite awhile, but due to their unique ambient garbage sound, they have remained very unpopular... this until they've decided to change their sound for a more Electro-Rock fusion style, that has finally gained them attention, though they still creep the odd track in that comes from their original style.