TCI, the U.K. hedge fund whose bid to increase its stake in J-Power was blocked by the government, bought shares in Mizuho Financial Group Inc. and Kajima Corp. to get major shareholders to prod the utility to boost returns.

The fund, officially The Children's Investment Fund Management (UK) LLP, bought stakes of less than 5 percent in Mizuho, Japan's second-biggest bank, and Kajima, the nation's biggest general contractor, in the past couple of months, John Ho, Hong Kong-based head of TCI's Asia division, said in Tokyo.

The London-based fund, with $10 billion in assets, invested in the companies because they are common shareholders of Electric Power Development Co., as J-Power is officially called, and will seek to hold them accountable on how they vote, Ho said. TCI is J-Power's biggest shareholder, with a 9.9 percent stake.