A multirotor aircraft is a rotorcraft with more than two rotors. Owing to its relatively simple mechanisms for flight control, it has been widely used in various fields, such as aerial photography and disaster management. To determine an optimal design for a multirotor aircraft, the geometric parameters and controllers are quasisimultaneously optimized. The domain of attraction, which defines the stable region around an equilibrium point for a nonlinear system, was used as an objective function for optimization. By finding geometric parameters and the controller that expands the size of the attraction domain, a multirotor aircraft can be optimized. The visualization of the domains shows that the optimized aircraft can deal with a larger deviation from an equilibrium point compared with the original aircraft.