Why would anybody want to become Japanese?

Inevitably the question of naturalization comes up on the internet forums related to living in Japan (usually under a visa or sometimes as a permanent (alien) resident), and people ask, given that naturalization requires a commitment when compared to commitment-less permanent residency status, why anybody would become Japanese? The answer, often by people who are not naturalized, is "the only reason you'd naturalize is if you want to vote or run for office." Another thing that foreigners (interestingly, it's rare to hear Japanese say this. More often you hear this from non-Japanese) often say in response to this is "you know that one will never be accepted as a Japanese" or "I could never give up my identity" — which misunderstands the point of "legally Japanese" in that in confuses the difference between nationality and race/ethnicity. Perhaps the confusion arises from the fact that the English (and Japanese) word can refer to all three of these very different concepts under the modern constitution of Japan.

Anyway, there are more reasons to be Japanese than to vote or run for office. To name a few:

1. Being a part of the government executive branch: Accessibility to additional jobs available only to Japanese (such as public sector jobs). While police officers and fire fighters are obvious examples, there are many other fields in the 公務員 {kōmuin} (public government worker) such as public school teachers that require citizenship. This can also mean access to sub-contracted jobs and assignments related to the above in sensitive areas of the public sector (intelligence, citizen's data, etc).
2. Potentially easier access to certain types of loans (a permanent link to the state with no links to other states makes you less of a risk from a credit-worthiness perspective). This is not a black or white issue; whether somebody can get structured or revolving credit in Japan is based on many complex variables, of which your residency status is just one of many factors. Just as there are many Japanese who are denied credit, there are many non-permanent resident aliens that obtain Japanese credit. But in general, having Japanese citizenship in Japan never hurts from the perspective of showing additional stability & reliability.
3. Depending on the limitations of your previous passport, a passport that has access to more countries without needing a visa. For people from the P.R.C. and some other countries who are business people and need to travel a lot, this is especially attractive. For example, I don't need a visa for short-term pleasure or business to China (something I do a lot), which I needed a visa for as an American.
4. Depending on the type of investment or business you're in, the structure of the company may need a certain balance of foreign vs nationals and/or foreign vs domestic capital.
5. The ability to sponsor other non-Japanese for certain situations requiring a Japanese sponsor.
6. Depending on your country, the taxation system may be better in Japan. This includes double reporting/taxation situations for Americans, lower taxes for Europeans, and better inheritance / death taxes depending on your country.
7. The ability to make it easier for your (present or future) family members to obtain Japanese visas, Japanese permanent residency, or Japanese citizenship (by birth through jus sanguinis or naturalization). Permanent residency can also help with this — except for citizenship.
8. The ability to vote in local and national public elections.
9. Being a part of the government legislative branch: The ability to run for public office (up to and including prime minister). There are already many examples of naturalized citizens who have served roles from city councillors to the Diet in the upper house (House of Councilors).
10. The ability to have a Japanese family register, a registered domicile: 本籍 {honseki}.
11. No worries about Residence Card (在留カード {zairyū kādo}) renewals or updates, changing or renewing one's Status of Residence (SoR aka 在留資格 {zairyū shikaku}), or re-entry permits into Japan. Ever.
12. The ability to have an official, legal, non-alias, Japanese sinogram/syllabet name that can be used everywhere in Japan.
13. No longer needing to have an alien registration card (ARC aka 外国人登録証明書 {gaikokujin tōroku shōmeisho}) or Residency Card (在留カード {zairyū kādo}) on your person and the (remote) possibility of being fined up to ¥200,000 for forgetting it.
14. The ability to abandon your previous nationality without being stateless.
15. The ability to have Japanese law and its constitution be directly connected to you (no matter where you may be in the world) may be more beneficial than your current laws and constitution.
16. If you're overseas and get into some sort of trouble (that is not your fault), the Japanese government goes to bat for you, as you are "one of their own."
17. The right to be judged by Japanese law exclusively; Japan does not extradite its own nationals to other countries, and instead tries them using their own courts and laws and uses their own punishment system.
18. The ability to receive welfare in Japan if you need it and meet the qualifications.
19. Being a part of the government judicial branch: The ability to take part in a jury as a "lay judge", being part of the Japanese justice system.
20. The unconditional irrevocable legal right to live in (and leave and return to) Japan at will. Permanent Residency status for aliens is close to this, but it can be revoked for certain types of crimes. And more commonly, it can expire if you need to go overseas for an extended period of time.

How much of the above is important or relevant to a person depends on their individual situation, of course. There are many people, depending on their lifestyle or current nationality, where much of the above would seem irrelevant, unneeded or duplicative with what they can currently do.

Citizenship doesn't just mean rights. It also comes with commitment and responsibilities (both current and future yet-to-be-written ones) by being linked to a state, so I don't recommend it as being something for everybody. Especially if you're already from a rich country like Japan where you're already entitled to first-world benefits and democracy or you are too attached to its ethnic culture or roots which are unlikely to exist in the same form in Japan.

For most people, permanent residency is close enough to this right and a good compromise (rights without the duties and responsibilities that comes with being linked to a different state), but "permanent" is not truly "permanent". Lots of PR people lose their PR status all the time by leaving Japan for an extended time.

I believe the actual reason that most people naturalize (including myself), however, has nothing to do with any of the above; the primary reason is much more prosaic than the lofty goals of being a sumo stable master or politician. Being legally Japanese gives you the right (in the literal constitutional "legal" sense) to be in Japan, no "if"s, "and"s, or "but"s: no matter if you forgot to renew your re-entry permit, no matter if you left the country for an extended period of time (which I've done), no matter if you don't have a proper passport (which I've also done by accident), and no matter if you've committed a deportation-worthy crime — although you may exercise part of that right to legally live in Japan while in prison.

For me, getting just temporarily displaced from Japan due to even a very unlikely re-entry permit screw-up which resulted in a loss of PR would be devastating to me, my family, and my career — both financially and emotionally. I've crossed the proverbial line in the sand long ago in that going forward in Japan, even when times are really tough, outweigh the benefits of the metaphorical home country "safety net," which would require starting over from scratch my life in my original country.