Is because of the sharp contrast between left and right ass.

Right ass is bigger and has wider hips, but it also looks a lot firmer.

Left ass is smaller, has malformed squishy flab on the right cheek and left cheek is saggy. Her butt is flabby and not round.

These characters are from the same series, and the erotic part is the difference. Instead of drawing their butts similar, the manga-ka draw them extremely differently.

Anyone else understand what I mean? The booty flab of left girl is cute as fuck!

http://www.strawpoll.me/11971179