UK driving licence help

I have been living in Japan for a year now driving on an IDP. I have a valid UK licence but have not spent 3 months in the UK since I attained the licence as I worked abroad for a year (while I worked abroad I also used an IDP). I now would like to get a licence to drive in Japan. Do I have to go through the same process as Japanese people do in order to get a Japanese licence, including paying the ridiculous fees for driving school? Or can I just take a test(paper and practical), the same as Americans? Any help would be greatly appreciated!

Do I have to go through the same process as Japanese people do in order to get a Japanese licence, including paying the ridiculous fees for driving school?

Unfortunately yes.

Or can I just take a test(paper and practical), the same as Americans?

No, the three month rule applies to them as well. They basically have the same requirements as you plus the additional requirement of the practical exam.

If there is no evidence in your passport that you left the UK for a year in order to work in that other country (some countries don't stamp passports anymore), but only a Japanese immigration stamp that shows the date of your entry into Japan that is more than three months after the date of issue of your driving license, you might be able to get a Japanese license without taking any practical tests.