I've recently returned from a trip across the country and liked everything about my (physical) ICOCA card, except that the machines used to charge it, at least the ones I've found, only accepted cash.
After charging it once with a decent balance though, I got away (almost) entirely without cash using it in combination with a virtual credit card via NFC, save for street food carts and Gachapon machines.
There are charging machines that accept cash cards / debit cards, but only those issued by Japanese banks. So cash is the only option for touristists. You can go completely cash-less if you can use mobile Suica / ICOCA, which let's you charge your phone with Apple Pay / Google Pay (with osaifu-keitai).
I did think it was kind of funny when I’d use a single machine to withdraw cash from my bank account and then deposit the cash right back in to load it onto my IC card.
After charging it once with a decent balance though, I got away (almost) entirely without cash using it in combination with a virtual credit card via NFC, save for street food carts and Gachapon machines.