This discussion is way off...
By default we can assume most AV idols has accepted money and/or gift and have sex with a man not her husband/bf/pick-up and not for a video shoot.
Do we call that prostitution? That's a matter of semantics. I think when most of you talk about it, you are thinking of almost totally open sex trade fuzoku or soapland or delivery health, basically any random Japanese man (forget foreigners lacking Japanese language and culture) with enough cash on hand can enter a establishment and have a go at a girl. If you want a particular girl, then you add more conditions, perhaps you have to be a repeat customers to that establishment (easy enough). The more popular that girl is, the more selection/conditions will need to be passed, here I mean any condition/requirement other than price point. Most important requirement is manner, culture, discretion and when you get into high end, social class, and at the top, you need connections.
Yes certain Western mindset says any time some money or gift is involved in a sexual relation it's prostitution (big exception being diamond ring (2 months of the man's pre-tax salary) for marriage). But reality, at least in the East, is much more complicated and interesting.
Courtesans are that strange oriental concept that's some crossing between prostitute, mistress and idol. I don't plan to get into it... but before you complain that it's the old way and the old way has died. I argue that it's not just nostalgia and tradition. I think it makes perfect business sense even in this modern world. A girl with some kind of fame or prestige (AV idol is enough qualification) and her associates (agent/pimp whathaveyou) can make a ton of money in the courtesan game, much more than in fuzoku or soapland, and certainly involving less work, troubles and exposure.
One key point about courtesans vs. prostitute is that there's no price. A girl can't advertise the price is ¥1,000,000 and will strip naked, give you a massage, rub your nipples and handjob/blowjob with condom, you can kiss my cheeks and boobs and butt with your lips, but no tongue or teeth. And you can fuck my pussy with your cock with condom on (but no fingers or tongue) until you cum once. And total time limit is 45 minutes. It doesn't work like that.
You just have to give gifts and show your devotion and negotiate with her handlers to try to guess what or how much is needed, and of course her handlers would never be so crass and rude as to tell you a price and tell you what "service" can be brought with that price. It's not even nudge nudge wink wink say no more, leave a million yen tip for this meal and next time she will show up and give you a good time. You really don't know how much money it's gonna cost you. All you know is she (and her pimp(s)) are milking you and she doesn't give a shit if you get frustrated and give up (cuz there are other suitors) you just get milked like a fool until you get lucky, or not.
So is a million yen credible or even meaningful? I don't think so. It may be enough or not, too high or too low. I don't know and I doubt anyone can say. Or will say, anyone who has experience in this game know that rule one is don't talk about the game.
As for Kirara specifically, the same writer who sell the million yen story also told the world that Kirara is independently wealthy. She is supposed to be a bit of genius at horse gambling and she has a life other than JAV and that's partly why she disappear from the scene randomly. She doesn't need monthly vids to cover her living expenses. Of course the writer also admit it's all hearsay so who knows, perhaps Kirara's wealth might even come from having sex with some extremely rich dudes. Perhaps she loses all her bets on horse but she doesn't care. All we know is that she is somewhat unique that she can disappear from JAV for a few months at a time but still maintain a top idol status releasing vids with prestigious studios and labels.
But I think the line about a million yen for a sex service with her is baloney. Not that the playno1 guy is making up a story but someone (perhaps Kirara or her agent) throws out a line and he dutifully reports the line. It's fair game, but believe it whatever you want to believe.