Nomura Holdings Inc. surged the most in more than two years in Tokyo trading after it announced a surprise ¥150 billion ($1.4 billion) share buyback along with plans to reduce its chairman's role to bolster governance.

Just days before its annual shareholders meeting, Japan's biggest brokerage said Tuesday that it will trim its stake in an affiliate that was involved in a damaging information leak and use the proceeds to fund the stock repurchase. The stock closed 11 percent higher on Wednesday, the biggest gain since November 2016, paring this year's decline to 10 percent.

Nomura's shareholders are scheduled to gather Monday, with one influential proxy adviser calling for the ouster of Chief Executive Officer Koji Nagai after the firm was penalized for leaking sensitive stock market information. Nagai is trying to restore investor confidence by cutting costs at its global investment banking and markets business and trimming retail branches at home following its first annual loss in a decade.