If you don’t have a Japanese credit card, you’re going to need to buy Japan Playstation Network Cards to purchase things like a Japan PS Plus subscription. Also, if you want to be able to buy digital games off of the Japan Playstation Store, this is the only real way to do so. The great thing is that it’s pretty straight forward. It is basically like buying a gift card.
The only real downside is that you have to choose from either a ¥1,000, ¥3,000, ¥5,000, or ¥10,000 card. What this means is that often you aren’t going to have exact amounts for what you want to buy and will always have a bit left over in your account. For instance, PS+ for a year is ¥5,143 which means if you want to buy a year subscription you either have to buy the ¥5,000 card + another card. Or simply buy the ¥10,000 card and have lots of money in your account left over. I actually chose to buy the ¥10,000 card just because I know there will be future digital items that I will want to buy. Like when they have digital sales.
Lastly, there are lots of places you can buy these cards online but I bought mine at Play-Asia. After purchasing my card, I received an email with my code within a few minutes. It is a very quick process!