Upvote:1
You could open a bank account in yens (or add a subaccount in yens to your existing account) and get a forex company offering international wires to exchange your USD and deposit the yens into it. This is very likely to be too big a hassle for a single vacation as the KYC regulations will make establishing a relationship with a forex company a bit of a process. But, if you are planning on spending many thousands, ten thousand and up, even, then it's certainly worth saving a couple hundred dollars.
Now to which company to use, that's not for this site to recommend. A very frequent answer would be Transferwise but they can only wire JPY to a bank account in Japan which is impossible to get without residency in Japan. And the card for their borderless account charges 2% for cash withdrawals. No win there. I love Transferwise to pieces but here they are not much of a help. A huge list can be found on https://www.finder.com/international-money-transfers/a-to-z-listing and they have a comparison tool as well but it doesn't take into consideration your special requirement of wiring JPY to the United Kingdom so even if you see a great rate that might not be available. With Transferwise out, I would (in 2019, this might get outdated) check out OFX and XE first but it's up to you to do the research. You now have three keywords to type into Google (OFX XE Transferwise), work from there.
Upvote:5
The worst you can do is getting out the dollars and using them in the UK to buy yen. You pay for getting your dollars changed to pounds and then you pay again to get your pounds changed to yen.
The slightly better option is to bring your dollar notes, gotten in the UK from your USA bank, to Japan, so you only have one set of exchange rates and costs.
Better still, use the US account to get yen out of the ATM in Japan. Check with the US bank if there is a best brand of ATM/bank in Japan for the lowest fees.
Why not use your card to pay direct in Japan?
Yes, they do still use cash more than in other countries. But most main hotels and many small ones do accept payment by card as do many of the restaurants.
You will want to have some cash, say enough for a couple of nights in a hotel and a couple of meals, and if you do not need it before, use that money for your last days in Japan.