Constructing dual-ion energy storage devices using anion-intercalation graphite cathodes offers the unique opportunity to simultaneously achieve high energy density and output power density. However, a critical challenge remains in the lack of proper anodes that match with graphite cathodes, particularly in sustainable electrolyte systems using abundant potassium. Here, a surface grafting approach utilizing multifunctional azobenzene sulfonic acid is reported, which transforms V₂C MXene into a high-kinetics K⁺-intercalation anode (denoted ASA-V₂C) for dual-ion energy storage devices. Importantly, the grafted azobenzene sulfonic acid offers extra K⁺-storage centers and fast K⁺-hopping sites, while concurrently acting as a buffer between V₂C layers to mitigate the structural distortion during K⁺ intercalation/de-intercalation. These functionalities enable the V₂C electrode with significantly enhanced specific capacity (173.9 mAh g⁻¹ vs 121.5 mAh g⁻¹ at 0.05 A g⁻¹), rate capability (43.1% vs 12.0% at 20 A g⁻¹), and cycling stability (80.3% vs 45.2% after 900 cycles at 0.05 A g⁻¹). When coupled with an anion-intercalation graphite cathode, the ASA-V₂C anode demonstrates its potential in a dual-ion energy storage device. Notably, the device depicts a maximum energy density of 175 Wh kg⁻¹ and a supercapacitor-comparable power density of 6.5 kW kg⁻¹, outperforming recently reported Li⁺-, Na⁺-, and K⁺-based dual-ion devices.