Empowering electrocatalysts with appropriate electrocatalytic activity is imperative to improve the electrochemical properties of lithium–sulfur (Li–S) batteries. Nevertheless, the intricate multi-step conversion pathways of sulfur concomitant with disparate electrokinetic processes make it challenging to establish a tried-and-true strategy to dynamically modulate the electronic structure of electrocatalysts and thus precisely catalyze the specific conversion step. Herein, a built-in electron reservoir is rationally envisaged to refashion the occurrence mechanism of synchronously coordinated electrocatalysis in bidirectional sulfur redox processes. As a proof-of-concept investigation, a facile incorporation of selenium (Se) into lithium polysulfides (LiPSs) is conscripted to recognize the inherent impetus for LiPSs reduction and Li2S decomposition. In conjunction with synchrotron-based characterizations and theoretical calculations, a streamline sulfur redox triggered by Se with a synchro-tuned electronic structure is identified. Specifically, the Se in LiPSs-Se could donate electrons to prompt ample LiPSs reduction in the discharge process, while the Se in the formed Li2S-Se functions as an electron receptor to extract electrons from Li2S for rapid Li2S decomposition in the following charge process. The proposed built-in electron reservoir offers an elegant avenue for dynamically coupling distinct electrokinetics via endogenic electronic structure modulation aiding in circumventing sophisticated interfacial architecture arrangement in contemporary multi-heterogeneous electrocatalysts.