Direct from the Overwatch Blog:
Specially outfitted for maximum fortification, Orisa is a four-legged robot designed by a brilliant 11-year-old engineer named Efi Oladele to keep the peace in Numbani.
Built from the scraps of the city's decommissioned OR15 defense bots, Orisa is still learning how to optimally perform her function. What she lacks in experience, she makes up for in her steadfast dedication to keeping her city—and her creator—safe from harm.
Orisa's main weapon is her rapid-fire Fusion Driver, an automatic gun with good range and accuracy even at a distance—though it comes at a cost, as Orisa’s movement slows down while she fires. Her alternate fire, Halt!, launches a graviton charge across the map, slowing nearby enemies as it passes, then pulling them toward it when it detonates.
Her Fortify ability boosts her personal defense, reducing damage taken and making her unstoppable for a short time. She can throw a device that creates a curved, stationary Protective Barrier, perfect for intercepting projectiles and shielding teammates. Lastly, as her ultimate ability, Orisa deploys a high-powered Supercharger that beams a buff to allies within its range, increasing the damage they can inflict on the opposing team.