23. Is there a ban on political parties engaging in commercial activities?

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)

第九条 政治団体の会計責任者は、会計帳簿を備え、これに当該政治団体に係る次に掲げる事項を記載しなければならない。機関紙誌の発行その他の事業による収入については、その事業の種類並びに当該種類ごとの金額及び収入年月日

Article 9 The accounting officer of a political organization shall maintain accounting books and record therein the following matters pertaining to said political organization.  Revenue from the publication of official journals and other business activities shall be categorized by type of activity, with the amount and date of receipt specified for each category.

There is no provision prohibiting political parties from engaging in commercial activities. Implicitly, parties can engage in commercial activities, as political parties should report revenues from the publication of official journals and other business activities.