Hello Hubbiida - and welcome to the forums!
In actuality, it is usually quite easy for a U.S. business with a U.S. signer to get approved for a merchant account.
However, I will point out the two areas of concern that would be present with your specific account:
(1) English Web site - most merchant providers require a Web site in English so that they can see what the site is actually selling. Thus, I'd suggest putting up an English version of the Web site to help facilitate this.
(2) Foreign Transactions - these are usually ok but the concern happens when a merchant does virtually 100% foreign sales as the risk levels are statistically much higher - often 8-10X higher.
In fact, since you will be marketing purely to a Japanese audience, you may even want to consider signing up directly for the JCB (Japanese Credit Bureau) card.
They may offer some standalone solution for this... here is their phone # - (800) 366-4522.
Hope that info is helpful!