Per Wikipedia here https://en.wikipedia.org/wiki/Japanese_Communist_Party#Ideology_and_policies :

[. . .] it is, however, politically moderate and advocates a peaceful transition to communism.[69] Marxism–Leninism, which former party chairman Tetsuzo Fuwa had worked for years to make acceptable to the electorate, was abandoned in favor of scientific socialism in 1976.[70][71] According to the Encyclopædia Britannica, the JCP became a more traditional democratic socialist party after modifying its policies in the 1990s.[57] This analysis is supported by the Japanese political scientist Kōji Nakakita [ja], who is often cited as a specialist on the JCP.[72] The JCP follows a Marxist ideology,[73][5] stating that the theory of Marx and Engels is the foundation of their program.[74] The party sits on the left[75] to far-left[80] of the left–right political spectrum.

I suppose the real answer is to read the material in Japanese and look at their policy decisions, but I for one don't have time for it (nor can I vote here in Japan anyway).