Hey hello95,
To do this you will need to have Multicurrency enabled - this is a feature of Essentials and Plus accounts and can be switched on by going to the Cog Wheel > Account and Settings > Advanced > Currency > Turn on. Please note multicurrency cannot be turned off once activated.
You can then select 'manage currencies' > 'Add currency' to add Japanese Yen to your list of currencies in QuickBooks.
To create an invoice in Yen, you will first need to set up the customer to make payments in this currency (you cannot edit this on an existing customer as each customer can only have one currency).
To create the customer, go to Sales > Customer > New Customer > Enter the details and select the 'Payments and billing' tab to select the currency under 'This customer pays me with'.
When you then select this customer when creating an invoice, this will default to show the currency in Yen.
You can see more on managing multi-currency in QuickBooks here.
Thanks :D
