Is there any other way to skip this koseki and get registered? cant i just get by as a US citizen as if i didnt have a koseki?
Not true.According to Japanese nationality law - Wikipedia ,
"A Japanese national is assumed to have renounced their nationality upon naturalization in any foreign country",
although the section does go on to say it's not -quite- as strict as that in practical application; it seems that if you didn't actively renounce your Japanese nationality, you still have a chance to retain it by renouncing your second nationality.
In any case, it's not going to be possible to get help as a citizen of both countries since Japan doesn't recognize that status. The best he can get if he persists is a chance to renounce his American citizenship before his loss of Japanese nationality becomes official. If the embassy brushes him off and leaves him in the gray area, that's actually doing him a favor if he might want to reclaim that nationality later.
(Oh, also, if he was born in Canada he may have Canadian citizenship already, and if he didn't renounce that citizenship and assert his Japanese citizenship by age 21 he may already not be a Japanese citizen. I'm not really sure how Canada treats immigrant birth and citizenship.)
Not true.
The keys words here are "assumed". You have to literally make the declaration of which nationality you want. I know quite a few people with dual citizenship who are Japanese. And there is no way of them finding out if you only use your Japanese passport in Japan.
I'm not saying there isn't a procedure to make a declaration. The existence of the procedure doesn't mean there aren't other ways to lose your citizenship.
And perhaps I am ill-informed. All I've done is carefully read the wiki page on the matter. If you think the wiki page is erroneous and misrepresents the actual laws and procedures, then bring it to them, I don't really care enough to comment again.
Oh, I am fully aware of the law Jus_soli. I am just replying to the statement you made that the Japanese government will know you have two citizenship's if you were born overseas, not all people(parents) will choose to have their baby have US citizenship even if it was born on US soil. My point being that there is no absolute way for the government to really know what your status is unless you tell them.Edit, postscript: Also, you seem to be ill-informed about U.S. citizenship. Yes, essentially all babies born on U.S. soil do become U.S. citizens, even the children of illegal immigrants are legal citizens. You don't have to do anything, it's automatic. Of course you can renounce it upon reaching legal age. Canada seems to be the same it turns out.
Apparently there's an exception for foreign diplomats, but of course, the Japanese government knows who they've sent here as a diplomat.
Automatic Birthright Citizenship: Who is an American? | Dominique Daniel - Academia.edu