The Bank of Japan's latest delay in reaching its 2 percent inflation target despite more than four years of aggressive monetary easing has cast a shadow over Gov. Haruhiko Kuroda's chances at a new term.

On Thursday the BOJ pushed back the timing of achieving the target to around fiscal 2019, the sixth time it has done so since Kuroda implemented the bank's ultra-easy policy in April 2013.

"(2 percent) is still an unrealistic target, even if they push the timing back," said Sayuri Shirai, a former member of the BOJ's policy-setting board who is now a professor at Keio University.