It's almost sad to say, but it's true. Nobody watches Karina for her looks. For JAV standards she's average looking at best. In a way that is sort of a good thing because the prettiest women in JAV tend to have big ego's. That means they can pump out videos that meet the bare minimum standards and still reach the top in sales and popularity. There's an understanding that chicks won't get any work or have a place in the industry if they don't do something drastic to make up for their lack of beauty. Even if an average slut puts out multiple anal scenes a month, they still won't get the kind of money the prettiest stars get. The prettier you are, the more privilege you have. You can film the same recycled scenes over and over and get paid more than even the biggest and most active anal whores.
Well there's a lot to unpack there. First don't make Karina Nishida to be a sad story, she had a pretty good career, almost 8 years as kikadan, a very respectable tribute-retirement vid (ok DAS is a third-tier studio, but also consider how often do you see third-tier studio do a retirement vid?)
Her look: meh I don't think anyone should feel pity for her. In the English fandom she didn't get attention, but in Japan, her haafu look is pretty popular.
Hot idols = big ego. Well you are mostly right. Rank/prestige seems to exclude anal. BUT I want to emphasis it's not idol's personal choice. It's the "culture" of the industry, ultimately I blame it on the fandom. Once an idol "un-ban" anal, her sustainable income will shrink in the future, the fandom will buy her less. It's utterly horrible. It's fandom, the industry that create this false slippery slope. (a slightly disconnected example, Shoko Takahashi's career was doing just fine, sure she stopped making the top-10 list, but she could keep doing the same "boring" JAV once a month. But for whatever reason, she "un-banned" creampie last October, which was fake anyway (all creampies are fake). And now what happen? She's retiring.
Mid range idol's income: actually we don't know about income. Someone like Karina Nishida may have made some good money without being in the top rank. The important thing is (1) number, (2) solo works. She got a very steady production rate, and mostly she's the solo girl on the cover. So her monthly income is fine. The exclusive contract girls, sure they get high profile prestige, but it's semi-open secret that their monthly income isn't in the top range. They have a rather relaxed work schedule (one or two filming days per month) and get treated with respect and most importantly they have (relative) job security.
In an industry where anal is relatively rare and even rarer among popular stars, you come to realize that beggars can't be choosers. So that being said, we honestly need more sluts like Karina. The top stars might be pornstars, but they're paid like supermodels and celebrities so they have no reason to do more hardcore scenes. Among them, there is a few elite women like Yua Mikami who are so popular and so well known that they practically get paid just to breathe. ... when you're that pretty ...
Now now I actually happens to be a big fan of Yua Mikami myself. Sure her sex scenes are super vanilla even pretentious, but she earned and everyday she is working very hard to earn her prestige and money-printing machine. Too bad, she will never do anal sex, life is life.
And a little secret: she is not pretty. Her beauty is man-made: a combination of plastic surgery, make-up, skillful camerawork, Photoshop and post-production. It's a lot of hardwork to be that pretty.
you'll gain the attention of rich politicians and businessmen. It's safe to assume that a good chunk of the top stars just film JAV as a hobby because the money they make fucking on camera is probably pocket change when compared to the money they can make fucking rich old geezers.
Now you are in tin-foil hat territory. I'm just gonna ignore this part of the conversation.
Eimi Fukada would be the most realistic candidate. I'm basing this primarily on the fact that she has that super depraved and curious daze like she is possessed by her desire to milk cocks while trying to find new ways to take herself to the next level. Her career also revolves primarily around the
Ahh... how to break it to you... Eimi Fukada is not a slut. Sure she is extremely good at pretending to be a slut, but that's only her persona; she is absolutely a pure professional.
Anyway how much she like or dislike anal sex has almost nothing to do with her ever doing one, a few or many anal sex title. Like (I'm convinced) no women ever enjoy swallowing sperm, she does it for other reasons, likely money.
Nishida, Fukada, Mikami: it's silly to talk about different degree of sluttiness. Each of them pick their career paths because of their assets, skills, circumstances and most importantly: market economy. Each of them is a professional and her own private sexual preference is not in the picture.