It was always ridiculously easy to get Japanese citizenship. 5 years of residency, don’t break any laws including traffic, pay your bills on time. Done.
It has recently been changed so that you now require 10 years of residency.
5 years. It's fairly easy to get. Sometimes it feels like half of the Beijing intelligentsia is in Tokyo now.
Lots of Chinese academics, engineers, investment bankers, and others shifted to Tokyo in the past few years. Even the kinds of salons and meetups you used to see at Tsinghua or Peking have almost entirely transplanted in Jimbocho based on my friends account.
It has recently been changed so that you now require 10 years of residency.
https://www.turning-japanese.info/p/misinfo.html