31. What are the provisions on 'ear marking' direct public funding to political parties (how it should be used)?

Source: 
政党助成法, 1994 (2022改正)
Political Party Subsidy Act, 1994 (as amended by Act No. 68 of 2022)

第四条　国は、政党の政治活動の自由を尊重し、政党交付金の交付に当たっては、条件を付し、又はその使途について制限してはならない。
２　政党は、政党交付金が国民から徴収された税金その他の貴重な財源で賄われるものであることに特に留意し、その責任を自覚し、その組織及び運営については民主的かつ公正なものとするとともに、国民の信頼にもとることのないように、政党交付金を適切に使用しなければならない。

Article 4. The State shall respect the freedom of political activities of political parties and shall not impose conditions or restrictions on the use of funds when granting subsidies to political parties.
2. Political parties shall be particularly mindful that party subsidies are funded by taxes collected from the people and other valuable financial resources. They shall be conscious of their responsibility, ensure their organization and operation are democratic and fair, and use party subsidies appropriately so as not to undermine public trust.

There is no provision about how subsidies must be used.