Did you bother to read the article that you posted?

"Foreigners over the age of 18 (or age 20 prior to April 1, 2022) may become Japanese citizens by naturalization after residing in the country for at least five years, renouncing any previous nationalities, and proving self-sufficiency through their occupation or existing financial assets."

You have to renounce previous nationalities, whereas the reverse the United States is much more generous towards the possibility of dual citizenship.