Obtaining japanese passport without koseki

I was wondering if I can obtain a Japanese passport without having a koseki. I was adopted from Japan to America by American nationals and was removed from my birth mothers’s koseki. I think I still retain Japanese Citizenship, but am not sure if I can obtain a Japanese passport without a koseki.

Contact Japanese embassy to check

if you have US nationality, I believe that you already lost Japanese nationality.

Thanks for the replies, I have yet to reach 22 years of age so by law I believe I still retain both citizenships because both citizenships was beyond my control. I'll contact the Japanese Embassy and confirm.

Have you looked at your adoption papers? You had to have a Japanese passport to enter the USA as a baby. Do you still have it? The Japanese keep great records. If you can find out your birth mother name and prefecture, you can probably find a relative. These are a lot of personal questions, but do not expect you to answer them here on the blog. They are just to give you ideas to find the necessary information. Also, many people retain both their USA and Japanese passports. They just “lose” or cannot “find” their other passport when they are suppose to surrender it.

Yes, I had a Japanese Passport as a baby but I was removed from the family's koseki after adoption. I'm not too informed on how koseki's work but I believe my name was crossed out from the koseki? Would a koseki with a crossed out name be accepted when presented at a Japanese Embassy?

Crossed of your family registers opens up a whole pile of uncertainty.

You realky just need to go to the embassy and see if you are still a citizen. Any further questions are a waste of time until you know the answer to the above question.

it depends on US law about adoption.
if an adopted child has no way to escape from getting US nationality (i.e an adopted child will have US nationality automatically in the adoption process), Japanese government may accept dual nationality until you become an adult.

1. the updating your koseki is your duty. there is a penalty, if you don't make your koseki newest.
2. your koseki was not removed (is present somewhere).
3. your koseki was separated from your mother(?)'s koseki and they made a new koseki, in which only you are a member.
4. since koseki is the record of Japanese nationality holders. you only can get an official copy of koseki. "without koseki" = "not koseki holder" = "not a Japanese"
5. koseki is maintained at city halls. not by Japanese government.
6. if you want to have a copy of your koseki, you need to know your "address", where your koseki is there. also, you need to know your name (written in Japanese) and your birth date.
7. you can ask パスポート申請情報開示請求, disclosure request of your information about passport application. I don't know the embassy may help it or not (probably not)
https://www.mofa.go.jp/mofaj/public/johokokai/passport/index.html
旅券（パスポート）の発給申請書の写し
if you have an expired passport, it may be helpful.
a typical example is:
https://www.pref.kanagawa.jp/osirase/02/2315/img/form_ippan_omote.png
(1) : your Japanese name
(3) : your "address" where your koseki is there.
8. since the information is private, only the passport holder can do that.
when the embassy does not help you, you may hire a professional (probably from abroad), who can do it legally instead of you.

Thank you, that was really helpful. I'll look into some of my old documents and figure out what to do from there.

I had a question regarding Ken's post, but where did you read that I would be assigned an independent koseki? I spoke to a few people who were somewhat acquainted with Japanese law and they said they haven't heard of this. If you could send a link or reference to where you found that information, that would be really helpful.

have you contacted an embassy or city hall yet?

I called them briefly and they said I should bring in a koseki because its the easiest way to prove citizenship in order to get a passport. Didn't talk in depth about my whole situation but I was planning on hiring someone in Japan to retrieve my koseki if I do have an independent koseki.

1. you never lose your Japanese nationality only by adoption. that is a law. reversely, if a foreigner is adopted to a Japanese, he/she will not get Japanese nationality automatically. (if US has the same system and you have US passport, you are no more a Japanese.)
2. all Japanese has their own koseki. there is no exception.
3. if you have a history of Japanese nationality holder, some record should be there. if not, you are (and were) not a Japanese.
4. even after death, dead Japanese have koseki records, which show their death.
5. there are at least two types of adoption systems in Japan. when the parents (or mother only) give their babies to unknown persons, generally they use 特別養子 system, by which it becomes harder to find blood relation.
【新本籍】には、縁組先の本籍ではなく、 追跡を難しくするためのいわばダミーのような戸籍（養子単独の戸籍）の本籍が記載されます。
i.e. you have a newly prepared koseki, but independent from your biological parents (or mother).
on the other hand, another system, 普通養子, is used to maintain their family. in many cases, it is done between relatives. in that case, a new koseki will not be generated.
6. in Japan, family tree (including adoption) is closely related to inheritance. adoption influences seriously.
don't want to make influence to inheritance : 特別養子.
want to make influence : 普通養子.

"I spoke to a few people who were somewhat acquainted with Japanese law and they said they haven't heard of this."
as already shown here, if you are (or were) a Japanese, you have your own koseki. "dependent or independent" is not your concern to get your final goal, passport.

please focus on your original purpose.

my post is a suggestion to consult a professional. since you already have him/her, you should get any advise from him/her, not from me