Fun fact: the Japanese government insists that foreigners use the name they have in their passport in official documents. That includes the middle name. My middle name has thus crept in all over the place. I've barely ever used it in my home country, but now have to use it everywhere (I live in Japan). Anyways, more relevant to OP, as a result, sometimes I'm called by my middle name, as if it were my last name (because the order is last first middle and they must assume that the literal last is the last name...)
I also live in Japan, and I have exactly the same problem.
I think the people with the biggest name problems in Japan may be ethnic Chinese. Many use the Japanese readings for their name characters in daily life, but some official purposes require the Chinese readings. Some Chinese also use yet another given name in English. I've had some friends who ran into serious problems proving they were who they were.
Addendum: Another problem that some people with Chinese names have in Japan is that the hanzi/kanji in their names do not display properly or at all in Japanese fonts, and even if the characters can be displayed they don’t have well-known Japanese readings, so people using phonetic input don’t know how to type the characters.
While we're here with fun facts. I've been living here for ten years, and haven't needed a registered seal until recently. To register my seal (using katakana) at the city hall, I needed to register my katakana name at the city hall too, which I never needed and had never done. How do you that? By presenting a somewhat official document with your katakana name, which none of the official IDs (resident card or driver's license) have. The document they would accept are a cash card or a passbook from a bank. How did the bank get my katakana name in the first place? I made it up. So what's the point? Who knows.
I had never realized how complicated it gets if two isolate languages just shared the script and some vocabulary, but independently developed syntax and pronunciation, until I took an introductory Chinese course. They insist "Akihabara" is obviously pronounced "chew-yeah, y'wan?(qiū yè yuán)", which hardly register as 3 letter noun to my ears.
And therefore, from your example, Japanese reading against Chinese reading, Chinese name in Japanese font, American name used for English against everything else, none of that is not just do not cross-validate but also seem somewhat fraudulent because everyone has some ideas about each of those strings.
(which, by the way, explains why made-up transliteration is fine; so long you're consistently a Linus Torvalds going by a close enough Ri-nasu To-baruzu, and no other versions exist, and it traces back to your passport, it cross validates as a coherent enough identity)
And Chinese names would be like "Ms. 3Jane Tessier-Ashpool" that seem to read "Saint-John Thomas Haywood" who's going by just "Junko Mary", nope, that isn't going to work on any official forms. I can only imagine how complicated it will be for them.
China also has this policy. Oddly enough, your middle name is often seen as part of your first name, so your first name is no longer “Sean”, it is “Sean Clarence”. Oh, and your last name is now two words because there is a space after the Mc in your passport to account for the non-standard capitalization.
That's funny, that would make it funny or awkward for me. While I don't have a middle name, I have 3 first names (as is customary in France: my first name, my godfather first name and my godmother first name). That means I have 2 male first name and a female one.
While some people use their second first name (it's rare but not unheard of), I don't know anyone who uses their third first name. In all but very official documents, you simply use one of your first name and your last name and that's it.
If I put my last name first and then my 3 first names, the female first name will come last. Let's just say no one has ever called me that, and I won't answer to it.
I'm French too. I said middle name because it was simpler. My mother has 7 (!) of them. I don't know how that would pan out for her. I don't know if they all appear on her passport, though.
