How to get a copy of a Koseki tohon?

please help me ! I am the child (I don't a have a Japanese passport)) of a Japanese dad who passed way 7 years ago.
How can I get a koseki , what I need to do ?

Getting a copy of a Koseki tohon (the person is already registered as a Japanese national, and need the paper that proves it)
and getting a koseki (the person is not yet registered as a Japanese national, and need to be registered as one)
are two different things.
Would you like to tell us what you need to do?

I would like to apply for The Japan Spouse / Child of a Japanese National Visa, but

the Japanese embassy in Germany says I need Current copy (not older than 3 months) from the Japanese family register (Kosekitohon), in which the family affiliation is made clear.

how to get that??

If you are Japanese (you do not state clearly, but inferred) then you do not apply for a visa. Just apply for the passport. You'll still probably need a copy of the koseki though.
Spouse/child of a Japanese national visa is for non-Japanese citizens.

If you are qualified for The Japan Spouse / Child of a Japanese National Visa, something about you should be written in your father's koseki.

Your father's koseki is kept at your father's "honseki" which is the address he registered his koseki to (which is not the same thing as his home address). You can either contact your father or contact the prefecture of that address to learn how to obtain a copy of that koseki. Details are also typically written in the prefecture's official website. In any case, you need to know the exact address of the honseki.

Note that just because he is your biological father, that doesn't mean that you are automatically on his koseki.

I hope you find whatever you need.

@JapanCustomTours

oh is it still possible to get a passport even when already am over 21 years old ??

oh is it still possible to get a passport even when already am over 21 years old ??

Well, I don't know what's going on on the OP's side, but I merely answered the question based on the fact that the OP's embassy told the OP to get a koseki tohon.

what legal evidence do you have which proves that you are a child of a Japanese ?
the answers against your question may vary depending on your evidence.

As I said in my comment, there was missing information in your original post, so I answered given that uncertainty. Now you are supplying more information so that changes things as others have noted.

@Uco

thanks you,

do you know where I can find my dads "honseki"??? does it Stand in his old passport??

his Registered domicile was Hokkaido

It's not written on the passport.

Ask your mother or your father's family.