1. Is there a ban on donations from foreign interests to political parties?

Source: 
政治資金規正法, 1948 (2022改正)
Political Funds Control Act, 1948 (as amended by Act No.68 of 2022)

第二十二条の五 何人も、外国人、外国法人又はその主たる構成員が外国人若しくは外国法人である団体その他の組織から、政治活動に関する寄附を受けてはならない。ただし、日本法人であつて、その発行する株式が金融商品取引所において五年以上継続して上場されているものがする寄附については、この限りでない。

Article 22-5 
No person shall receive donations related to political activities from foreign nationals, foreign corporations, or organizations whose principal members are foreign nationals or foreign corporations. However, this shall not apply to donations made by Japanese corporations whose issued shares have been continuously listed on a financial instruments exchange for five years or more.

Political contributions from (1) Foreign persons, (2) foreign entities, or (3) associations or any other organisations of which the majority of the members are foreign persons or entities are banned, with the exception of Japanese entities that have been listed on a Japanese stock exchange consecutively for five years or more.