NaNbO3 (NN)-based lead-free antiferroelectric (AFE) ceramics with ultrahigh energy-storage density (Wrec) have attracted increasing attention for applications in high power electronic devices. However, large polarization hysteresis induced by the AFE-ferroelectric (FE) phase transition tends to cause high energy dissipation. In this work, a relaxor AFE orthorhombic R-phase ceramic in (1-x)NN-xCaTiO3 ((1-x)NN-xCT) solid solutions was found to show outstanding comprehensive energy-storage properties with giant Wrec = 6.6 J/cm3, high energy efficiency η = 80% and ultrahigh power density PD = 350 MW/cm3 as × ≥ 0.14. The results of Raman spectrum, Raman mapping and transmission electron microscopy demonstrate that introducing CT in NN will moderately enhance the local-structure inhomogeneity as compared with many other complex perovskites, thus benefiting the gradual transformation from AFE microdomains to AFE nanodomains with increasing CT content. This allows the polarization saturation to be reached at a relatively high electric field. Of particular importance is that the high band-gap in NN and CT, refined grain size and suppressed dielectric loss enable obviously enhanced dielectric breakdown strength. As a result, the proper balance between those different factors leads to an obvious improvement in the overall energy-storage performance of the AFE R-phase region. The above results demonstrate that the local structure engineering is expected to play a crucial role in the achievement of excellent energy-storage properties in NN-based lead-free relaxor AFE ceramics.