Thanks! Documentation states "You can add credit and prepaid cards to Apple Pay on iPhone 7, iPhone 7 Plus, and Apple Watch Series 2 to make payments in stores using QUICPay or iD." https://support.apple.com/en-us/HT206638 Good to know that prepaid doesn't seem to work, yet.

I spent part of yesterday hunting around for a Japanese sms enabled sim other than Softbank or Telecom Square's Wi-Ho, which both have voice prepaid sim (barely) obtainable with visitor visa. Wi-Ho seems to have a fixed 14 day expiration. OCN and IIJMio have data + sms, no voice sims on monthly subscriptions meant for the domestic market which may allow sign up with a (foreign) credit card. No identity card needed. I guess they take the resident restriction on voice pretty literally rather than as a phone number. Line's MVNO requires identity verification for their data and data + sms sims.

A non-expiring no min contract data sim, sms, and a few other ways to carry currency seems useful for repeat visits.