The contradictory relationship between band gaps and the second-harmonic generation (SHG) response constitutes a formidable challenge in the rational design of infrared nonlinear optical (IR NLO) crystals. In oxide-based crystals, the incorporation of strongly distorted octahedra containing d° cations as central elements are a common approach to enhance SHG responses, while inadvertently leading to a significant decrease in band gaps due to the unfavorable energy level splitting. In this study, an innovative "4d/5s electron band-inversion" strategy is introduced to enhance SHG response while preserving a wide band gap within the octahedron-symmetry-protected langasite structure. A novel high-performance IR NLO crystal, La