additional info Taking a break from our usual flow, I thought I would post this interesting article from MSN this week. It talks about how ancient roman coins were found under a Japanese castle.
http://asect.org.uk/?ilyminaciya=%D9%85%D9%88%D9%82%D8%B9-%D9%84%D8%A7%D9%8A%D8%AA-%D9%81%D9%88%D8%B1%D9%83%D8%B3&a06=68 Clearly, there was no trade or interaction between the Romans and the Japanese in 400 AD (logistically this was nearly impossible at the time).
web link The most likely explanation here is that a European trader brought these old coins over with him to Japan. And somehow, someone (European or Japanese) brought them to Okinawa Island.
website here Without reading too much into things, oftentimes the most simple answer is the best one…