Getting the money into Japan to buy a car was a very stressful experience with comparing prices and finding a method I felt comfortable entrusting a large sum of money with. The method I came up with was not one that I found anywhere in any of my research, and I think it's the cheapest, safest method possible. Hopefully this helps someone in the future. :D
So, I went to try TransferWise, and for whatever reason, they deactivated my account and refused to give me service. They weren't able to provide a reason for why they weren't able to help me.
However, I'm kind of glad because I found that in my case, a standard wire transfer was much cheaper than a 3rd party money exchange company like Transferwise or OFX. ALSO, if you use the money for something like buying a car, those companies apparently need to keep records of what you bought, and it becomes a complicated process. You have to send in documentation, talk to people on the phone, etc. (and OFX ended up not being able to help me either, they can't help you if your address is in Japan).
Wiring the money through my American bank was done in 2 minutes, and I didn't have to talk to anyone, which was a nice bonus.
Steps I took:
Open a bank account with Shinsei bank. (if you're an expat living in Japan, trust me, this is the one to get. They can hold US dollars in addition to Japanese yen, and they have zero fees for receiving international wires (most Japanese banks will charge you))
Wire the money directly from the bank account in your home country (a $40 fee is pretty standard, which is an awesome price if you're transferring a lot of money) Give explicit instructions to NOT convert the money into yen. (banks normally try to kill you with their horrible exchange rates)
When the money arrives in your Shinsei bank account, convert it to yen though their online portal. It can be done in about 60 seconds and is immediately available for use.
As a reference, the total fees I was charged were about half that of Travelwise, and the money arrived just as fast or faster than it would have. The fee looked something like this:
$40 fee for wiring the money (flat rate regardless of amount)
~0.08% fee (1/10 of Transferwise's rate) for exchanging money through Shinsei bank (it is a special introductory rate, but the standard rate is still excellent)