To propel advanced energy storage devices for high pulse power systems, overcoming the pivotal challenges of concurrently augmenting energy storage density (Wrec) and efficiency (η) in relaxor ferroelectric (RFE) ceramics is imperative. This study delineates a stagewise collaborative optimization strategy aimed at enhancing the energy storage property (ESP) of BaTiO3 (BT)-based (Ba0.8Sr0.2)TiO3 (BST) ceramics, namely, integrating (Na0.73Bi0.09)NbO3 (NBN) with secondary processing technology. Capitalizing on the inherent strong polarity from A-site Bi3+ ions, the high valence, and wide-bandgap of B-sites introduce local random electric fields and impede the transition of electrons, generating polar nanoregions and expanding breakdown thresholds. Furthermore, the application of the viscous polymer process (VPP) in BST-NBN ceramics seeks to diminish porosity and enhance compactness, thereby sequentially improving polarization difference (ΔP) and breakdown strength (Eb). Guided by a stepwise optimization strategy, the anticipated energy storage characteristics (Wrec = 8.5 J/cm3, η = 93.4 %) under 640 kV/cm are realized in 0.91BST-0.09NBN-VPP ceramics, ensuring thermal reliability (20–120 °C) superior to most BT-based ceramics. This research marks a substantial advancement in the pursuit of more efficient and reliable ceramic dielectric capacitors, cruscial for powering modern high-power electronic devices.