Just to share the knowledge :-

I installed an app off the Japanese app store called Giftee.

Its interesting because it specialises in low value gift certificates.

The ones of interest are -

Family Mart
Lawson
Basket Robbins
Starbucks

You can buy gift certificates with Apple Pay - I was able to use the app to buy a 500 yen Basket robbins certificate in English settings with my UK card via Apple Pay.

The app is currently running a promo where you effectively get what you bought again for free - I now have 2 x 500 yen Basket Robbins certificates to use XD.

Obviously there is NO ENGLISH but for those who can navigate the app its a convenient way of paying for low value purchases if youre prepared to navigate it.

-mrploddy