@jtjtitutsjtghiog good on you for planning your dream and reaching out for guidance.
I live in Australia so can't really help you but since we have moved a lot around the world I will share my thoughts, before directing you where you can find MNetters who live in Japan or Korea , and this is in a section called Living Overseas.
I will report your discussion so it will be moved here:
www.mumsnet.com/Talk/living_overseas
Someone who went through the process and immigration might be able to give you more info.
Most countries use a point system and also look for very specialised job skills.
Going straight to a country is harder than being invited with a job offer.
Working for big companies with subsidiaries around the world , is sometimes a way to use the back door to enter the country, when you have moved internally and the company will deal with visas and relocation.
Or you are specialised on a specific UK/American brand more than a Japanese brand, so for example you are a highly skilled mechanic for Harley Davidson. Foreign luxury or specialised brands of cars, usually import their mechanics, so if you are not too focused on motorbikes, think Rolls-Royce, Bentley, Aston Martin, Lagonda, Land Rover, Jaguar, McLaren, Lotus, Mini, MG, and Morgan.
Think also spare parts specialist, logistic manager, ..... which still belong to the motorbikes even if not hands on.
I think working as a mechanic in Japan for Honda, Suzuki and other Japanese brands, might not be so easy.
You need to decide which country and start leaning the language because being fluent will certainly help.
The points also often increase with the years of experience, so you should start looking for part time work now, maybe even unpaid for a day a month.
IF you google work permit + Japan/Korea you will get a flair, by reading documents like this one:
qz.com/1127891/moving-to-japan-do-you-have-the-points-to-qualify-as-a-resident/
My last piece of advice is to look for cultural association such as Japan House in London, and if you live near, maybe volunteer in a couple of years
www.japanhouselondon.uk/support/volunteer/
If you don't live near London, you can find regional association her www.uk.emb-japan.go.jp/itpr_en/japanorg.html
Networking , building contacts will help you one day.
Good luck and study hard because excellency will help you.