A small group of banks are handling the "financial" side of billion-dollar fintech start-ups. : Instead of trying to beat a wave of high-growth financial technology startups at their own game, a group of small banks is opting to join them. These low profile community banks quietly run the plumbing underneath billion-dollar fintech firms like Square, Stripe and Robinhood — handling mundane banking activities for them like holding customer deposits and underwriting loans — while the tech firms remake finance for a digital age. For some, it's a match made in heaven.