Unless you use Apple Pay, then you can get the Suica or Pasmo card app to your phone. Then you can use credit card in your Apple Pay to load money to the Suica or Pasmo card, otherwise you will still need Yen cash to load the traffic card or to buy metro/train tickets.
Unfortunately Suica or Pasmo card app does not support Android phone.
On top of that, many smaller shops / eateries, do not take foreign credit cards. Of course if you largely only spend at high end places and have Apple Pay, then you do not need Yen cash in most cases.
Otherwise, just get the Yen at any 7-11 ATMs with a 0% foreign transaction fee debit card, such as a Fidelity or a Schwab debit card. I believe some Capital One's bank accounts also have 0% forex fee debit cards.
