Kaho Shibuya, I think... And her size in that pic has been exaggerated by the camera angle, as Hitomi outboob her by a respectable margin.
Yep and, yep, it's Kaho and, yep, Hitomi 'outboobs' her by a considerable amount. I won't spend much time on Kaho because I don't find her at all attractive. She works on being cute and busty rather than erotic and busty as Hitomi does. I guess it suits her.
BTW, they did a couple of shots which are more representative of the size difference and you can find them on Hitomi's Twitter. I've got something better to post when I get past my 24 hour embargo.