Hi,
As you are a UK resident in receipt of foreign income from property, you are required to file a Self Assessment tax return and declare the income.
However, you will need to complete a foreign income supplementary page and claim Double Taxation Relief against the tax paid abroad, which prevents you from paying tax twice.
You can find further guidance here:
DT10650PP - Double Taxation Relief Manual: Guidance by country: Japan: Contents
Thank you.