The Bank of Japan's unprecedented review of its unprecedented monetary policy has stepped up focus on a key group of Gov. Haruhiko Kuroda's allies.

A trio of top officials in the Monetary Affairs Department, led by Executive Director Masayoshi Amamiya — referred to by some as Mr. BOJ — is leading the initiative, according to people familiar with the process who asked not to be named as the discussions are private.

Personnel from other important areas within the bank have been asked to report frankly on what has and hasn't worked in efforts to achieve 2 percent inflation, the people said. Those include the Financial Markets Department that conducts the bank's massive asset purchases, the Financial Systems group that monitors the banking industry and the Research and Statistics Department.