The Bank of Japan is a week away from a vacuum at the top as the opposition-controlled Upper House on Wednesday voted down the government's bid to replace BOJ Gov. Toshihiko Fukui with his deputy of five years, Toshiro Muto.

To avoid the first postwar top-level vacancy, the government and Liberal Democratic Party-New Komeito ruling bloc must either persuade the opposition camp to back a renominated Muto or find an acceptable candidate before Fukui exits on March 19.

The Democratic Party of Japan, the largest opposition force, argues that handing the top spot to a former vice finance minister puts the BOJ at risk of falling under the sway of the government.