Landing Arm Holdings’ giant initial public offering is a coup for Mizuho Financial Group, one of the four global investment banks leading this year’s biggest deal. Now the Japanese firm needs to prove that it’s more than just a one-time thing.

Many within and outside Japan’s third-largest bank see winning the role as a reward by SoftBank Group founder Masayoshi Son for the decades of loyalty and financing that the lender provided to his telecom-turned-tech investment behemoth, which is selling a stake in chip designer Arm.

But Mizuho has also been building its dealmaking credentials in the United States through its team led by Michal Katz, head of investment and corporate banking at the New York-based unit. Katz was deeply involved in the Arm deal, people with knowledge of the matter said.