50. Do third parties have to report on election campaign finances?

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)

第四条　３　この法律において「寄附」とは、金銭、物品その他の財産上の利益の供与又は交付で、党費又は会費その他債務の履行としてされるもの以外のものをいう。

Article 4. 3. In this Act, “donation” means the provision or delivery of money, goods, or other property interests, excluding those made as payment of party dues, membership fees, or other debts.

Spending by a third party is regarded as a donation, or the provision of money, goods, or services.  Therefore, even though such third parties do not have to report election campaign finances, parties and candidates have to report third parties' spending made on behalf of them (as noted in 48 and 49).