An interested person (meaning a person other than a requestor for review who is found to have an interest in the disposition related to the request for review or the disposition related to the inaction, in light of the provisions of laws and regulations that serve as the grounds for the disposition; the same applies below) may participate in the request for review by obtaining permission from a review officer.
A review officer may request an interested persons to participate in the request for review when it is found necessary.
The participation in the request for review may be entrusted to an agent.
審査請求への参加は、代理人によってすることができる。
Each of the agent referred to in the preceding paragraph may perform all acts concerning participation in the request for review on behalf of the person who participates in the request for review pursuant to the provisions of paragraph (1) or (2) (referred to as an "intervenor" below); provided, however, that the agent may conduct procedures to withdraw the participation in the request for review only when they have been specially entrusted by the requestor.
Read this with the articles around it