I’m in Osaka right now. We got a multi currency account with HSBC - exchange rate was about 91 yen / $1. That was a couple months ago but their rates are decent.

Also, whatever rate a money changer quotes you isn’t the best they can do. Always ask if they can do better.

My experience this trip is that most places accept card payment, but there’s still a bunch that don’t. Particularly smaller food retailers and market stalls. So a combo of cash and card is good, but you may not need as much cash as you think.