FWIW I've been using Suica on a Japanese Garmin smart watch and refilling it with Google Pay on an international card without too many problems (and before that with Apple Pay with the same card on iPhone/Apple Watch), although there are probably some gotchas (Apple Pay at POS seems to be pretty hit and miss for in Tokyo and I've never figured out why).
FWIW I've been using Suica on a Japanese Garmin smart watch and refilling it with Google Pay on an international card without too many problems (and before that with Apple Pay with the same card on iPhone/Apple Watch), although there are probably some gotchas (Apple Pay at POS seems to be pretty hit and miss for in Tokyo and I've never figured out why).