Regulating the molecular/electrolyte interface is crucial for improving aqueous zinc-ion batteries (AZIBs), particularly for organic cathodes that often suffer from dissolution, sluggish interfacial charge transfer, and insufficient cycling stability. Herein, inspired by the C=N zinc-storage sites in phenazine-based cathodes, a fully conjugated pyrazine-linked organic cathode, DQPAT, was rationally designed to regulate molecular aggregation and cation-binding interfaces. The fully conjugated backbone integrated C=N sites and electrochemically activatable C–O groups within an extended π-conjugated framework, enabling multi-site Zn²⁺/H⁺ co-storage through reversible C=N/C–N and C=O/C–O redox couples. The extended π-conjugated framework promoted intramolecular electron delocalization, while ordered π–π stacking facilitated intermolecular charge transport and suppressed molecular dissolution at the electrode/electrolyte interface. Consequently, DQPAT delivered a high capacity of 561 mAh g^-1 at 0.05 A g^-1 and retained 90.3% capacity after 20,000 cycles at 10 A g^-1. Notably, the electrochemically oxidized state (o-DQPAT) reached its theoretical capacity under ultralow active-material loading, confirming nearly complete utilization of a twelve-electron redox process. In situ/ex situ analyses and theoretical calculations revealed a coupled Zn²⁺/H⁺ adsorption/desorption mechanism. This work demonstrated an interface-oriented molecular design strategy for developing high-capacity and long-life organic cathodes in AZIBs.