18. Is there a limit on the amount a donor can contribute to a candidate?

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)

第二十一条の二　何人も、公職の候補者の政治活動（選挙運動を除く。）に関して寄附をしてはならない。

第二十二条 個人のする政治活動に関する寄附は、各年中において、政党及び政治資金団体以外の同一の者に対しては、百五十万円を超えることができない。

Article 21-2 No person shall make a donation in connection with the political activities (excluding election campaigns) of a candidate for public office.

Article 22 Contributions to an individual's political activities shall not exceed one million five hundred thousand yen per year to any single person other than a political party or political funding organization.

There is a limit on the amount a donor can contribute to a candidate.  While donations to candidates are restricted outside campaign periods (Art. 21-2), contributions made during permitted periods are subject to an annual limit of 1.5 million yen under Article 22 of the Political Funds Control Act.