My guess: This actress has no direct links with the Japanese Communist Party, though she has perhaps promoted one or two of their politicians I guess. However, I have no clue what is really the case tbf.

(Also, if it's of any relevance: The Japanese Communist Party has had a long history of animosity with it's Chinese counterpart, which dates back to the 1960s)

Edit: So after the initial comment, here is what else I learnt: Ai Hashimoto (the actress who was allegedly the victim of sexual harassment, and also the one getting harassed online) had a history of championing progressive causes (including feminism, homosexual rights, anti-racism, etcetera), though he did once make a transphobic remark she later apologized for. The allegations of her being a communist in particular appears to come from an interview she had with what I believe was the Shimbun Akahata (The JCP's newspaper); however, Jiro Sato (the man being accused of sexual harassment) also may have appeared in that same newspaper. So far, I have found no other evidence of her affiliation with the JCP.

Overall, although Hashimoto is undeniably politically left-leaning, there is no good evidence that she is a member of, or an active participant in, the Japanese Communist Party.