thank you so much about this .There are two categories : toned ass and fat ass. Both look completely different. One category is all about the harmony, fitting the girl's body (slender in general), with a round shape. Examples are Mukai Ai, Amakawa Sora, Nishimiya Yume, ...
The other category, fat ass, is just all about being big, shape is different (to say the least), cellulite on thick legs and ass cheeks and bodiess are like Tsukasa Shiori, Fujisawa Rio, ...
And Shinoda Yu lost her ass a while ago, with her weight loss. She's skinny for at least 3-4 years.
nice example too