Article 22-6., "Anonymous donations or different name from identical person are prohibited. However the restrictions is not applicable to donations collected by political parties/political fund organizations on the street or in a meeting hall (the amount must be less than 1000 yen)" (Source: Political Funds Control Act, 1948 (as amended by Act No. 135 of 2007))
7. Is there a ban on anonymous donations to political parties?
Yes, above certain threshold