Yes, Japan Partner Inc. is quite real. I happened to be at their office 2 weeks ago.
The issues that stems at the heart of this debate though is purchasing from a exporter vs purchasing from a importer. There's a lot of leg work and sleepless nights involved in both sides of the journey but one of them is much safer and far more user-friendly. For example, if you purchase directly from an exporter you better make sure you read their fine print because many of them have little sections that will say you are not entitled to any refunds or they will say they reserve the right to issue refunds within 6 to 12 months following your refund request. That is to say that you're purchasing from a real exporter and not just sending money into a black hole in another country. The other part of this is they are only the exporter meaning once the car is on the boat or in a container the rest is up to you (see my last comment below). Also keep in mind that it's very difficult to know if the exporter actually owns the vehicle they are potentially offering to you. For all you know it could be a car that doesn't exist or may belong to another exporter and they are just using it to generate and dupe people into borked sales agreements. A common thing they like to do is get you to send them money and then tell you someone else bought it before you did and they'll look to find you another car so you can't get your money back.
So that leads us to purchasing from an importer, where you now have a legal binding sale agreement and contract which you can seek legal assistance to help enforce if there's any issues. This is something you otherwise can't take advantage of from other sources outside the U.S. As well, if the importer is doing things properly they will be a licensed dealer which again gives you yet another legal protection if something goes wrong. Where people fall short and end up in bad situations is when they buy from straight middle-men off of Facebook or some other location, where the person has no legal establishment, no company, no place of business, no license to operate, etc. and you hand that person your money hoping to get a car in return. There's many well established places out there who have invested a lot of time and money to do things the right way, I recommend you seek out one of those places to trust your money with so you get your car the proper way.
Lastly, there's the DIY route which ties into the purchase from exporter option. While yes it is possible to accomplish this you should really stop and ask yourself the hard questions, do you want to gamble with your money and your car? If you want some milk do you go seek a cow and extract the milk yourself or do you just go to the supermarket and purchase a carton to drink? When you want to play a video game, do you just create your own video game or do you go buy one that some company made? If a hurricane rips apart the roof on your house do you teach yourself to and then fix or replace the roof yourself or do you simple call someone who's qualified to do it for you? I can safely tell you that when I need something done and I'm not a professional at it then I'll just cut to the chase and hire or pay the right people to do the job. That's not a sales pitch, it's just common sense
Look at it this way, you can venture on the import journey yourself and hope you do things right but you could put yourself in a situation when you miss 1 step or mess something up and you'll be paying fines between $5,000 and $40,000 to the government all over a car you probably paid $10,000 for or less in Japan. Is it really worth it? Are you really going to save that much money? You'll still have to pay local sales tax and all other applicable fees involved. The only thing you'll save is paying a importer's T&M (time and material) fee but is that really worth your time? Again, most people have lives, jobs, and other important things to worry about instead of trying to self-educate to do a 6 week process on your own only to save $500 in most cases. Is that really worth it or do you just pay a real company to deliver what you want for you so it's done the right way?
Back in the day when I attempted to import my first car I thought I was going to be slick and do it all on my own. Well, I did it and to tell you the truth it was more of a hassle then I wanted it to be. I had to use up vacation time at work, put important projects on hold while I was out. I burned through tons of money on transporting the car myself. I had to pay a nice little fine because the car arrived dirty. Then I spent countless hours of my life arguing with state DMV workers trying to title the car. In the end it was a huge pain in the a** I would have rather paid someone else to do so I could of carried on with my life and just waited for the car to be delivered to me. Now I own a company that does that sort of thing. Ironic I suppose.
Hope this helps.