Insufficient exposure and utilization of active sites often induces an inferior reactivity for transition-metal-based two-dimensional (2D) materials. In response, we for the first time propose a universal “nano-tailoring” strategy to incorporate abundant defects and active sites into low-crystallinity nanosheets by electrochemically leaching of Al species. With MnAl layered double hydroxides (LDHs) as a representative example, potassium-birnessite MnO2 (AK-MnO2) with oxygen vacancies and abundant edge sites is successfully produced. The oxygen vacancies are shown to help optimize the electron-transfer and ion-adsorption capability. These integrated advantages endow the AK-MnO2 with a high capacitance value of 239 F g−1 at 100 A g−1. By further combining with soft X-ray absorption spectroscopy techniques, we unravel that the reducibility of M2+ in M2+Al-LDH serves as the key descriptor for the reconstruction rate. This “nano-tailoring” strategy can provide some important implications and clues to manipulating 2D materials for efficient energy storage and conversion.