Nickel-based materials are promising anode candidates for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) due to their high theoretical capacities. However, their practical application is hindered by slow ion diffusion kinetics and structural degradation during cycling, resulting in rapid capacity decay. To address these limitations, we developed a sulfur/selenium (S/Se) dual-anion engineering strategy that creates strong interfacial charge redistribution through S2−/Se2− synergy, thereby accelerating charge transfer kinetics and stabilizing the electrode-electrolyte interface. Using a one-step microwave-assisted synthesis (20 minutes), we successfully fabricated NiSSe nanoparticles embedded in nitrogen-doped carbon (NiSSe/N-C). The NiSSe/N-C anode delivers ultrahigh reversible capacities of 1006.2 mAh g−1 at 0.2 A g−1 and 756.4 mAh g−1 at 5 A g−1 over 3000 cycles in SIBs, while achieving 530 mAh g−1 at 0.2 A g−1 and 477 mAh g−1 at 1 A g−1 over 200 cycles in PIBs. When paired with a NaNi0.33Fe0.33Mn0.33O2 cathode in a full-cell configuration, the NiSSe/N-C anode enables 96.7% capacity retention after 200 cycles, demonstrating its practicality in pouch cells. This work highlights the dual advantages of microwave-driven rapid synthesis and multi-anion synergy for designing high-performance battery materials.