When Takahiro Mitani's term as head of the world's largest retirement fund finishes in March, so too will the old era of Japanese pension management.

The former Bank of Japan official saw his power ebb during a five-year reign at the ¥131 trillion Government Pension Investment Fund, as Prime Minister Shinzo Abe took office with the goal of overcoming deflation.

Mitani, 65, will be the last person to wield sole control of a bond-heavy GPIF after the biggest overhaul in the fund's history.