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Dreams are there to be pursued, even when they are a long shot. (If the will exists, there can be a way.)
Zen10101, i picked up from your tone that because of your foreignness, and probably you are a Caucasian, perhaps American, that your racial and natiional background might present advantages for you. Based on the stories of such foreigners who have lived in Japan that I've come across in the forums, I am now generalizing the Japanese are proud, and as with any group of humans, have prejudices against those outside their tribe. Ironically - if what I picked up about your tone was correct, your alien nature will probably work as an additional roadblock.
But that does not mean those doing the hiring can't get past their possible biases, in fact some may look upon you as an exotic oddity which could work in your favor (and that is what I guess you were counting on). Luck would play a factor in this area.
If you can achieve fluency with Japanese, you may be able to remove hurdles, so you are on the right track there.
Organized crime had a headlock on U.S. porn once - if what the producer of DEEP THROAT claimed on a documentary was true, he did not see the millions of dollars that breakthrough movie had produced - but that was back in the theatrical age, when Mafia goons could strong-arm theater owners. With the advent of the Internet, control was lost. I don't think you would need to worry about the Yakuza, using similar logic. (That does not mean they haven't muscled in on the production, rather than the distribution end, but even if they turn out to be the secret power behind some JAV company, that does not mean one morning you will wake up with a horse's head.)
As to how one gets a job as a director in any arm of the movie industry, let's think about how that process works in the U.S. ... if we are talking about Hollywood, you can't expect to walk in (well, you can't just walk in, period) and get handed an important position - in short, as Suvlaco put it, you would have that proverbial "snowball's chance."
I would imagine the U.S. porn industry would not be as rigid as the studios in Hollywood, but the bigger porn companies probably operate as a microcosm of Hollywood, as the pron industry has become a cookie-cutter sort of big business operation (in contrast to the quirky independents of the 1970s). If you manage to get an appointment and get to see a honcho from a major porn company, you can't tell them that you would like to be a director and expect them to give you a job.
They have already got their personnel. I would imagine JAV studios would be even more difficult, judging by their small pool of male actors that they keep using again and again. I'm guessing there would be more of a loyalty aspect at play, making it tough for anyone to break through to their ranks.
Casshern2 mentioned scripts, and if you can offer amazing new ideas, no doubt they would be open to them. (Your fluency in Japanese would need to target writing as well as speaking, should you choose this direction - unless you hire a translator.) But then they would want to buy the script. You can always pull a Sylvestor Stallone on them (he would not let go of his ROCKY screenplay unless he starred in the movie), and demand the condition of directing, but you may not be able to pull this gambit until a few sold scripts, or unless your first script is truly exceptional.
A director needs to have a reel. To get that reel, you would need to put in various clips from your hired jobs. If you have never been hired, then you would need to produce the films yourself.
If you present them with a reel that shows amazing talent, they might still be reluctant to entrust you with a real job; yet you were again on the right track with your suspicions about starting out with a lesser job. I don't think the position of "assistant director" would even be available in low-budget porn (not that an assistant director does what the director does, an A.D. mostly coordinates), so you might be confronted with the lowest rung on the ladder, that of production assistant, or "slave." The risk of working your way up then becomes how do you elevate yourself from a lowly production assistant to a director. That would take time, and luck.
The fastest track to becoming a JAV director is to save your yen (or the currency of your country) and to produce a porno. As producer, you give yourself the job of director. The idea would be to try and get your porno distributed by the JAV companies, and as they get ideas about how beautifully you handle yourself on "celluloid," they may start thinking about hiring you.
But imagine yourself in a foreign country, not knowing anything about the ins and the outs of negotiations and legalities, not knowing anything about Japanese psychology, and giving yourself the position of a film producer. Not that it can't be done, but it will be a hard nut to crack to say the least, if the idea is to wind up with professional results.
Short of that, the remaining option would be to approach the miniscule and not the major JAV makers. You would probably have to work for free, but if you can somehow get yourself at the helm, you can then take finished film to the majors as your reel; you would then have something to offer them, instead of saying, I am a high and mighty American, and you would be doing yourselves a favor by making my inexperienced self a director.
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