The banks themselves get the best exchange rates. So Visa tends to have the best ones at any moment in time. Instead of changing money back and forth, I’ve been taking out money via credit card. I’ve made sure that my bank doesnt charge me extra for it though. You can take out money at basically every 7-11 and Family mart via the ATM. You might get charged something like 108 yen if you take out 10 000 yen, but I think that offsets the exchange pain in the necks. Also, I try to pay for most things with the credit card, but that’s not always possible. That said, you will need some cash when you get to the airport so maybe have something like 5000 yen (7k yen for 2ppl) on you and take the rest out via card.
Just my two yen.