Sea's under-the-radar fintech business could lead the giant to new heights.Sea Limited (SE 0.03%) is best known for two things: Shopee, its e-commerce giant that dominates Southeast Asia, and Garena, the once high-flying gaming business that's showing signs of a comeback. But under the radar, Sea has been steadily nurturing a third business that could one day rival its other companies.That business is Monee (previously known as SeaMoney), Sea's fintech arm. While investors often focus on Shopee's market sha ...