To address the challenges of sluggish ion transport and severe volume fluctuation in potassium-ion batteries (PIBs) arising from the large K⁺ radius, we design a covalently bonded V₅S₈/Sb₂S₃ heterostructure encapsulated in N-doped carbon (V₅S₈/Sb₂S₃@NC). Calculations using density functional theory (DFT) show that the metallic V₅S₈ and semiconducting Sb₂S₃ form a bandgap-free interface, facilitating rapid charge transfer, while the V–S–Sb covalent bonds enhance interfacial stability. Where V₅S₈ undergoes partial (de)intercalation-induced amorphization that relaxes lattice stress and buffers the ∼300% volume expansion of Sb₂S₃ to only ∼112% (verified by in situ optical microscopy). The synergistic design delivers a high reversible capacity of 657.6 mA h g⁻¹ at 0.05 A g⁻¹, long-term cycling stability with 301.5 mA h g⁻¹ retained after 600 cycles at 1 A g⁻¹, and rate capability superior to most reported PIB anodes. This work highlights the critical role of covalent interface engineering and amorphization-regulated K⁺ storage for high-energy PIB anodes.