Greenhill's 75th-place ranking for global mergers advice this year didn’t deter Mizuho Financial Group from paying more than double the market price for the U.S. boutique bank.

Facing rock-bottom interest rates and lackluster returns at home in recent years, Mizuho and some of Japan’s biggest banks are seeking to make inroads into the world’s largest fee pool, even if they have to pay a premium for the assets.

Sumitomo Mitsui Financial Group last month agreed to triple its stake in Jefferies Financial Group, while Mitsubishi UFJ Financial Group, Japan’s biggest bank, has a more than decade-old alliance with Morgan Stanley.