How many people have naturalized to Japan since the beginning of history?

Naturalization, being the acquisition of Japanese nationality not from birth, has been a legal procedure in the Nationality Laws of Imperial Japan and the State of Japan.

As of 2015, a total of almost 581,000 people have become legally Japanese since the fall of the shogunate and the rise of constitutional "westernized" Japan.

Because being a Japanese national is defined by law (by Article 10 of both the Meiji Constitution and the modern constitution, naturalization events are recorded by law and accurate data is kept. The graph above is a visual depiction of the recorded data. Some notes:

• Under the Meiji Constitution's nationality law, over a period of about eighty years from 1868 to 1951, a total of only 333 people became Japanese subjects. That's an average of 4.4 people per year.
• Individual year statistics do not exist for the fifteen years from 1951 to 1966. During this period:
• 41,151 Koreans naturalized (average of 2,743/year)
• 4,320 Chinese naturalized (average of 288/year)
• 1,461 "others" (neither Korean nor Chinese) naturalized (avg. 97/year)
• The Ministry of Justice did not begin tracking applications until 1969
• The Ministry of Justice did not begin tracking rejections until 1989

Although its not possible to definitively link the cause, we can correlate many historical events to peaks and valleys within the data:

• 1950 is the year the Nationality Law was re-written (including new rules for naturalization) for the new "peace" Constitution that was enacted in 1947 for the State of Japan.
• 1972 was the year that the People's Republic of China was recognized by the U.N. over Taiwan. the Republic of China. In comparison, Hong Kong suffered a large spike in renunciations after the handover of sovereignty from the UK to the PRC and the Tienanmen Square Massacre.
• 1985 was the year the naturalization law was revised, allowing those whose fathers were non-Japanese to inherit Japanese nationality from their mother by birth.
• 1989 was the year the real estate speculation "bubble economy" in Japan collapsed and the TSE crashed
• 1990 was the year Japan began inviting up to 3rd generation Japanese-Brazilians and other "Nikkei" (日系 {Nikkei}) to Japan for legal work
• 2002 was the year North Korea admitted to kidnapping Japanese children; a serious blow to the reputation of Chongryon leading to its bankruptcy, decline in enrollment, and closing of many DPRK affiliated schools in Japan
• 2008 was the Lehman Shock and the beginning of the worldwide Great Recession
• 2009 was the year Japan began offering airfare stipeds aimed at Brazilians and other South Americans who wished to emigrate
• 2011 was the year of the Great East Japan Earthquake
• 2013 was the start of Abenomics to improve the macro economy

I am aware that there are some foreigners who were recognized and given legal "status" and class/rank by the various shogunate governments in the 19th century before the Meiji Restoration and thus could arguably be considered to be "legally Japanese", but the data above, including those who became Imperial Subjects of the Empire, reflect those who became legally Japanese due to the nationality laws enacted under Japan's two constitutions.