14. Is there a limit on the amount a donor can contribute to a political party during a non-election specific period?

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)

第二十一条の三　政党及び政治資金団体に対してされる政治活動に関する寄附は、各年中において、次の各号の区分に応じ、当該各号に掲げる額を超えることができない。
一　個人のする寄附 
二千万円
二　会社のする寄附
五十億円以上
三千万円
十億円以上五十億円未満
千五百万円
十億円未満
七百五十万円
三　労働組合又は職員団体のする寄附
十万人以上
三千万円
五万人以上十万人未満
千五百万円
五万人未満
七百五十万円
四　前二号の団体以外の団体（政治団体を除く。）のする寄附
六千万円以上
三千万円
二千万円以上六千万円未満
千五百万円
二千万円未満
七百五十万円

Article 21-3. Donations made to political parties and political funding organizations for political activities shall not exceed the amounts listed in the following items for each year, according to the respective categories:
(i) Donations made by individuals
¥20 million
(ii) Donations made by corporations
¥5 billion or more
¥30 million
¥1 billion or more but less than ¥5 billion
¥15 million
Less than ¥1 billion
¥7.5 million
(iii) Donations by labor unions or employee organizations
100,000 or more members
¥30 million
50,000 or more members but fewer than 100,000 members
¥15 million
Fewer than 50,000 members
¥7.5 million
(iv) Donations by organizations other than those specified in the preceding two items (excluding political organizations)
¥60 million or more
¥30 million
¥20 million or more but less than ¥60 million
¥15 million
Less than ¥20 million
¥7.5 million

There is a limit on the amount a donor can contribute each year.