For me, I'd exchange it for local currency->USD-JPY or local currency->JPY at a forex kiosk (whichever has a better return).

If I was bringing a lot of cash, I'd do 60% JPY, 40% USD. I was thinking for my 2-week trip of bringing ~$1000CDN or ~$1000USD equivalent of JPY (whichever gives a higher return during exchange) then just ride the rest on card.