Every single provider that claims to be Japanese is Korean....LOL.  I'm racking my head thinking of one and can't...at least not yet.  Will let you know when I find one, good luck in the meantime.

depends on how you define thin and young...check out mayumi (careful there are two mayumis in NY)...perhaps not the greatest gfe, but highly skilled

...but the girls are almost always Korean.  It's just like the Consumer Electronics Show -- Samsung, Samsung, Samsung.  Whatever happened to Sony?

There are a couple of Japanese agencies that have been run by Japanese, however, the clients they take have to be Japanese as far as I know.
You can find those ads on the Japanese free paper that you will find at SUSHI BAR, or Japanese restaurant, though you need to read Japanese and to make up as to look like Japanese.

First off, Haya at Jungle Jane's is half Japanese, half Korean, so with her, your halfway there. (Sorry, couldn't help myself. I get so punny at times.) Also, if you can track down Mika from Julie's, she's Japanese. But most Caucasians can't really see or tell the difference between Chinese, Japanese, and Korean, although I know that Asians can. So why? I really don't know of many Caucasians who want a German girl, not a French girl. Usually, there is the insistence on being able to understand and speak English. It's tough enough finding a good Asian provider, why the need for sushi rather than kimchi?

will post if I find any japanese treasures.