The geometric complexity of human motion hinders efficient biomechanical energy harvesting, as varying directions and amplitudes of movement often cause misalignment between harvesters and external excitations. To overcome this limitation, we present a self-aligning mechanism, similar to a self-spooling pulley, to enhance the performance of biomechanical energy harvesting. The mechanism enables the internal driving direction to adaptively align with the external excitation, improving energy-harvesting effectiveness and minimizing wear. The self-aligning and energy-harvesting modules can achieve motion angle and amplitude sensing by integrating triboelectric nanogenerators (TENGs) on their surfaces. The electricity generated by the embedded electromagnetic harvester (EMH) powers the TENG-based self-sensing module, realizing a self-powered monitoring system. One demonstration shows a 46.91% increase in average power at a running speed of 9 km/h compared to the system without the self-aligning mechanism.