Freelance for foreign company Working Holiday

After a thorough internet research I'm still confused.
I'm on a Working Holiday visa in Japan right now and have been told, that both employed and self-employed work is an option. Unfortunately, I don't know what taxing rules apply, when working self-employed for a foreign (/American) company. (I'm German and not an American citizen.)
I won't make much money with the job, it's a part-time, minimum wage job and the income will be transferred to Paypal /my German bank account. Of cause, I will use a small amount of that money in Japan, but the largest amount will stay in Germany or go to companies outside Japan (like AirBnB, a company in Luxembourg).
Do I have to tax my entire income regardless or only the amount transferred to Japan? And if it's only a small amount transferred to Japan, do I have to pay taxes, even though it's only around 200-300 Euros per month?
And what percentage do I pay if so?
Also, how much work is it to register a freelance job in Japanese offices and will it be complicated to file the tax reports yourself? (I'm not sure it's worth a huge effort, if I don't make much money with it anyway.)

(Regarding German taxes, I would probably easily stay under the year's maximum amount I can earn without having to pay income taxes at all.)

Loving regards from Kyoto,
Nadja

As a resident of Japan who is carrying out work in Japan you are subject to the same tax laws that anyone else is.

I'm not sure it's worth a huge effort, if I don't make much money with it anyway.
Not worth the effort if you avoid getting caught. I highly recommend just paying what (if anything) you owe.

As a resident of Japan who is carrying out work in Japan you are subject to the same tax laws that anyone else is.

And these are for you as a non-permanent tax resident: you don't need to pay taxes on income that does not get sent to Japan.

do I have to pay taxes, even though it's only around 200-300 Euros per month?

Unless you have more than around 500,000 yen of taxable income per year, you don't pay income taxes.

And what percentage do I pay if so?

If you earn more than the exemption of around 500,000 yen, then the rates are the same as for everybody else, as explained here:
https://www.japan-guide.com/e/e2206.html

Also, how much work is it to register a freelance job in Japanese offices and will it be complicated to file the tax reports yourself? (I'm not sure it's worth a huge effort, if I don't make much money with it anyway.)

You don't need to "register" freelance jobs. Filing tax reports is quite complicated, but with just 200-300 Euro per month, it won't be necessary.

if they pay money for your working hours, you are "employed".
if you and they make a contract to complete a certain project and you get money, you are self-employed.
in the first place, you can't choose "employed" or "self-employed".

for example,
"self-employed",
the work is "making something" and you can get 100 yen, if you make one item. the contract must determines the price per item.
they will pay money how many you made. when you made 100 items, they will pay 10000 yen. they don't consider how many time you spend your time to make 100 items. if you made them in 10 hours. you earn money 10000 yen by 10 hour working. if you make it faster, you get more money. you can get a rest at any time, if you want, because your work is independent from the company.

"employed". they hire you (for example) 1000 yen per hour. the contract must determine your hourly wage (or daily wage, etc.). they will pay money depending on how many hours you worked for. even when you only make 50 items for 10 hours working, they still pay you 10000 yen. when you made 200 items in 10 hours, they pay you 10000 yen only.

if you get hurt when you are working,
"employed" , you are insured by labor insurance. (and you are protected by labor law. you are not a slave.)
"self-employed", getting hurt is your personal problem. it is not the company's responsibility.

"employed", you can get at least 1080000 yen deduction for income tax.
"self-employed", you can get 480000 yen deduction for income tax.