It is possible to naturalise after 5 years of residence in Japan. This is shorter than the 10 years required in principle for permanent residency.
However, Japan does not permit citizens to hold multiple nationalities, and requires those who naturalise to relinquish any other nationalities they may hold.
The benefit of naturalisation is that Japanese citizens live in Japan by right under the constitution. Compare this to permanent residency, which is permission from the government to reside in Japan that can lapse or be revoked.
Naturalising may make the holder liable for the exit tax.