I think especially someone like Yu who also has a great ass.
Here we go again ... Those "porn experts" need to be more objective and stop spreading lies. Her ass, even more for the last maybe 2-3 years, has nothing special, tons of girls have better a looking butt than her. And I'm not talking about a fake giant ugly ass like Maria Nagai.
So the "great ass" looks like that.
I just picked a random name I know, Hanazawa Himari. I don't follow her, so I'm not biased at all. She isn't advertised as having a nice butt or anything like that. However, her's has a better shape in the same outfits.
Always the same names over and over again ... I'm sure if a top of the best asse sin JAV was published, she would be in with let's say, Kurea Hasumi (ok, fair enough for her), Yuki Jin (same thing), June Lovejoy (lol, she's fat, the other aren't), Maria Nagai (plastic monster with fake ass), Eimi Fukada (another alien-looking girl).
The industry changes and new girls are coming. If you are a "JAV expert", you should take a look at the new girls too. I like a nice round, toned, butt on a girl (again, I'm not talking about the fat girls with giant cellulite trailer looking butts), and except Kurea and Yuki, none of the other would be elligeable. There are many new girls, some are exclusive with big studios, it's not difficult to find them. Again, just a name, not a girl I follow, Yamagishi Aika. Slender girl, toned body, nice round toned butt, look way better than Yu Shinoda.
Not only that but I think their body types compliment each other quite nicely given that Yu is very much a twig these days whereas Waka has got some meat on her bones.
Waka just turned into a fat cow after her comeback. She was already not slender at her debut, but her body curves were still noticeable. Now her legs are like tree trunks and her boobs melted into her belly fat.