27. Are there provisions requiring donations to go through the banking system?

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)

第二十二条の六の二　何人も、政治資金団体の預金又は貯金の口座への振込みによることなく、政治資金団体に対して寄附をしてはならない。ただし、その金額が千円以下の寄附及び不動産の譲渡又は貸付け（地上権の設定を含む。）による寄附については、この限りでない。

Article 22-6-2 No person shall make a donation to a political funding organization without transferring funds into the organization's deposit or savings account. However, this shall not apply to donations of one thousand yen or less, or donations made through the transfer or lease of real property (including the establishment of surface rights).

A donor should use a bank transfer if a donation is more than 1,000 yen.