Personally i thinks that breast in the JAV industry are far less common that in western porn. American porn in particular.
I don't get why some people think that sora aoi breast are fake. To me they seem and have always seen 100% real. I know some people point out that their too firm and big for her body frame. but you have to remember that no two women are the same, just like no two breast are exactly the same. even in the same pair. Sora was just bless with large firm breast. Sora Aoi bust size has also change over the course of her career. When she first debut they were larger than during the high of here JAV career. during the high of her career they where still huge but notably smaller, but not much samller. by the end of her career they where even smaller but still amazing beautiful. the shift in her bust size can be attribute to her weight lost. At Sora Aoi debut she was thicker but still had a slim body, during the high of her career she lost a noticeable amount of weight. i don't know how much but i would assume around the range of 5-10 pounds. This weight lost reduce her breast size but mainly turn her body frame type from average to slim. At the end of her career sora aoi lost more weight, which to me is why her breast are even smaller. By these point i guess that sora aoi lost much weight possible with out effecting her bust size much. which is why any further weight would greatly affect her bust size than before. Which is by her breast size decrease further. well that's my two cents.
Also i don't know why anyone would even consider Yuma Asami breast could be fake. yes she has a slim body but she not supermodel skinny. her breast are large and look so soft :inlove:.
personally i think that Kirara Asuka, Momoka Nishina, Haruka Sanada breast are real. I haven't seen anything in picture or video to consider otherwise.
Kirara Asuka breast match her body type, which is slim to average. Her body remeinds me of a young Sora Aoi.
I'm not much of a fan of Momoka, but again her breast are huge and match her body. She a thick girl than Sora Aoi or Kirara Asuka so i can easy see her having larger breast than either one of them. Also unlike most super busty JAV idols Momoka's breast are firm compare to the usual large, soft and at times shapeless.
As for Haruka Sanada. her body is amazing. She has a curvy body and her breast are huge and soft yet firm enough to give them a nice shape a look to them.