Ai no Kusabi universe leaves a lot to our imagination. Some things can be guessed from bits of information we are given, about others we can only speculate. People asked many questions about AnK. Based on those questions I tried to form some answers. These are just my theories and guesses, not to be taken too seriously. But perhaps someone could find them useful.
There is a point of view that Iason was an android, is this true?
When Iason had his legs cut off, in the anime it was shown very closely what he had inside and it was human flash and bones, nothing else. It was also described closely in the novel the same. Elites were entirely organic. They were humans very perfect humans, maybe even mutated into perfection, but still humans.
Yoshihara does mention androids in a few places of her novel, but she describes them as something different than the elites. There were androids on Amoi (nothing more is said about them, I have a theory that they might be among other things Jupiter's personal guards) and there were elites. They were in a way close (we can assume that the androids were more or less organic/cloned as well), but still different.
There are also a few places in the novel when the elites are indeed identified with the androids, which confused me at first as well. But as far as I remember now, this only happens in the Bison's conversations, so in fact it's the mongrels who confuse matters or simply don't care about calling things their proper names, and this time I think Yoshihara did it very purposely to show those boys ignorance.
Do we ever find out what the secret of Tanagura is?
The secret of Tanagura concerns Tanagura's cooperation with Ceres' Guardian. There is a fragment in the novel, in chapter 3 where Katze tells Riki about his conclusions and discoveries. Here we go:
"(...) I guess you didn't know either that the Breeding Centre in Ceres, Guardian, is secretly directed by Tanagura. (...) I know it's hard to believe, but think about it for a minute. (...) the chance of male versus female birth is about fifty fifty. There's no way to explain the low percentage of female births other than someone secretly manipulating it. Especially since this has remained the case from generation to generation. Tanagura... is controlling the population. (...) Nevertheless, the number of mongrels must neither increase nor decrease. The slum and us, mongrels, are necessary to feed the superiority complex of the citizens of Midas. We are an example of the fate that awaits those who disobey and who forget that love and passion are prohibited emotions."*
It's however not said how exactly the population was controlled. What we know is that there was a laboratory hidden in the underground part of Guardian and that its existence was classified as top secret. (When Kirie discovered it by accident, it caused quite a stir in Tanagura. It became a point of great importance to catch the kid and get rid of him. That's the main reason why Kirie was taken care of in the novel.)
And of course Tanagura taking mongrel boys for Eos furniture is another part of the cooperation, although if this particular fact was confidential is not clear. Riki didn't know about it, but come to think about it, something like this could not remain a secret for long too many people knew about it (all elites, furniture, former furniture, Guardian bosses...).
Are there any other planets in the Amoi solar system?
"Twelfth planet of the star system of Glan, Amoi, was a small, remote planet, not even visited by delinquents wanted by the law. It had no natural resources or intelligent life"*. That's how things looked before the first settlers arrived on Amoi, but of course their arrival didn't change anything in the scale of the star system. So we might assume that:
a) Since Amoi wasn't a very friendly planet and the scientists chose it anyway, it was probably still most friendly in the whole system of Glan and the only one that could be terraformed. Moreover, there was probably no other intelligent life on the other planets of the system, otherwise Amoi would have been a point of great interest as a perfect place to establish a base for scientific research (and well, it's simply not needed for the plot). In short, there were many planets in the system of Glan, but only Amoi was inhabited.
b) Little is said about other worlds that maintained contacts with Amoi. Since it was a remote planet, we can assume that those contacts were rather scarce. Yoshihara mentions one planet that Amoi had business with Laocon of the system of Veran, but that's the only world I remember (but well, I don't know the whole novel by heart, I could forget about something ;-).
c) There was a big spaceport in Tanagura and in the anime we can see that it was quite busy. At one moment in OVA2 Riki says that a trip by shuttle to a place called Daars (never mentioned in the novel) takes only one day. I can't imagine any spacecraft (not even the most advanced one) capable of crossing the distance between two solar systems (not even the closest ones) in one day. Maybe it is simply a mistake of the anime authors, but that brought me to a conclusion that Amoi had space colonies. Nothing like that is mentioned in the canon, but it doesn't interfere with it either, even if it's not Rieko Yoshihara's vision. About Amoi's space colonies we can read for example in Becca's Wasteland/Fortress and in my On Hire/Delivery.
Is the rest of Amoi inhabited?
Yes. Another fragment: "Normally, free cities formed confederations, and maintained themselves through bargaining relations in political and economic matters, but, although as city-states, they were independent, not many of them functioned with total autonomy. Small cities that lacked mostly natural resources, and did not have any notable industry, were absorbed by larger metropolises, and in effect they were no more than semi-colonial dependents for which the name of 'federated' was no more than a title. In the middle of all that, not belonging to any federation, not permitting any outside interference, not folding to any pressure, was Tanagura."* (It is made clear, however, that Tanagura strongly influenced the other cities.)
So, there were no countries on Amoi, there were city-states, like in Ancient Greece. We might assume that they shared the same language and currency, but whether they shared customs and the system of social classes is not clear (i.e. it's quite possible that elites and pets existed only in Tanagura).
But is the rest of Amoi inhabited? There's a notion that outside its cities Amoi was a wasteland. It's not mentioned in the novel, but there are hints to it in the anime. We can see that the areas surrounding Tanagura and Midas are open plains without greenery. Of course it can't be the basis to say that all Amoi looked like that, still it gives us an idea. Besides, it seems logical. The easiest way to terraform a planet would be to limit the process to city areas, the rest leaving as it was, or adapting just slightly. You could live there, but these weren't favourable conditions. Wastelands, wastes, deserts appear in quite a few fanfics (Becca's Wasteland/Fortress, Shayne's The Other Side/Doppelganger, my On Hire/Delivery) and I'm their true supporter.
Were there female elites?
I don't remember female elites mentioned anywhere in the novel, but neither do I remember any mention that they were not there. In the anime there are a few frames showing individuals who look like females, but with anime you never know all characters are androgynous. It's not even clear whether those figures are elites or not. Besides, the anime authors changed quite a few details as compared to the novel, so this could be one of them. For me, personally, female elites don't fit Yoshihara's universe, but I might also think of a few reasons why they should be there. So all in all I can only say that there are no indications in either way and that I simply don't know. It depends on each fan's personal view.
According to Lupin Gang's intro to the OVAs an owner releases their pet after 1 or 2 years. But in the anime Katze says that pets 'fall from one brothel in Midas to another until they die'. What with it?
Lupin Gang were actually fans, just like us. Those days AnK was still very exotic and the information in the Internet very scarce first of all there was no novel translation, so they probably knew about Yoshihara's universe less than the average fan knows today. They made some factual errors in the intro (like the one about the hair color). This is probably just another one of them, based most likely on the fact that after 1 or 2 years the elites did release their pets meaning that they discarded them, but they did not free them.
Here is what Raoul says about it (in the novel): "The rules say that pets whose term has expired should be reprocessed or sold to Midas."* More or less Katze's words. Come to think about it, freeing pets wouldn't make much sense if what Katze says is true, that they had 'brains of mosquitoes' and were mostly addicted to aphrodisiacs. Most of them wouldn't be capable of living on their own (and even if some were, who cared to give them the chance?). Why cram Midas with such cripples since secondary pet market posed such a profitable alternative?
So, after their time in Eos expired, pets were sold, not released. Usually they went to Midas brothels, or, in case of the younger, prettier ones, and especially those most expensive from the Academy, probably to another private owner some lesser elite or rich Midas citizen. Maybe that's what Raoul has in mind by saying 'reprocessed'. Of course after the second master, or maybe even the third one, they eventually landed in the brothels anyway.
Are elites born as infants or created as adults?
I think elites are born like ordinary people. Otherwise it wouldn't make sense they would be deprived of a very important period of life when a man learns all concepts of the world and acquires most of their skills and knowledge. And the elites are supposed to be superintelligent. Probably there were some boarding schools for the young elites, where they lived and received education, until they became adults and were released to the outside world to take their due posts.
Do elites grow old like ordinary people or slower?
No information is given about it. For a very fangirlish reason I would like to believe that they grow old just as fast as other people. Because if an elite pairs with a non-elite, it would be nice if they aged together instead of one looking at another growing old. ;-)
What happens to the old elites?
Have you ever seen an old elite in the anime? No. Elites are the fine face of Tanagura (or the whole Amoi), they must be young, beautiful and flawless. Any trace of growing old would be inappropriate.
Does that mean that the elites don't grow old? I don't believe that. Are forbidden to show up in public? Maybe imprisoned somewhere? Closer, but still not quite...
I guess it was Shayne who came up with this idea... How about a paradise for elderly elites? A city. Or even better somewhere outside the planet, a colony for example. A place where the elites can peacefully retire. They can still wallow in luxuries they always lived in, without needing to work. Once you reached a certain age, say 40, you go there and live an easy, careless life till the end of your days.
A happy picture, isn't it? Or maybe not so happy at all... What if you don't want to retire at the age of 40? What if you still feel young, fully fit for work and eager to continue your career. And they practically throw you out. All because you have barely visible crow's feet and a few gray hairs. You have to leave your home, your work, your friends if you have them. You're not banned from your hometown, you're not imprisoned anywhere, but if you want to come back for some reason (say, to take care of some matters) that must be for short and you better don't show up in public places.
It seems the gentle but nevertheless ruthless way that fits my idea of how Jupiter might handle her beloved children once they're past the prime of their prime. Of course it's also possible that aged elites did live in Tanagura and were simply not shown in the anime, just like for example Onyx elites and Midas citizens, but the former version seems way more appealing. Moreover, it opens very interesting possibilities for fanfiction. ;-)
What happens to furniture whose time in Eos expired?
The fate of ex-pets is no secret. But what about furniture? What happened with them? About that nothing is said in the canon. I guess the main question is whether they were just dismissed and no one gave a damn what happened to them, or they had some ultimate benefits, like being granted citizens' rights.
I'm inclined to accept the optimistic version. Why? Because there had to be something that compensated the castration and made it worth being a faithful elite minion for a few years. The prospect of returning to Ceres and with such past had to be ghastly and would never stir up any sense of duty in those mongrel boys. And anyway, would a former furniture be accepted back in the slum? I truly don't think so. Besides, Katze says in the novel that he was condemned to living in the black market. Mongrels were in general condemned to it, so that confirms the idea that furniture met better fate.
Thus my conviction that once their time in Eos expired, they were granted citizenship and even given their former masters' references (although their past and origins were made clear to everyone). With that, they could look for a suitable job in Midas usually in some club or brothel where they could be hired as guards and custodians of the 'other' employees. But maybe some really lucky and spirited ones could find something better than that. A 'decent' job.
* All quotes in this article are taken from the fan translation of the novel (hard-cover edition). The translation was made by Shabriri Lin, Shiromori and San-chan.