Small-strain stiffness is key in geotechnical applications such as machine foundation design, soil response under earthquakes, and liquefaction assessment. Typically defined at strain levels below 10⁻4, small-strain stiffness is considered reversible and anisotropic. Many constitutive models describe soil behavior, but most elastic formulations rely on hypoelastic frameworks, which can conflict with thermodynamic principles. These models also often treat the elastic domain as isotropic. The reversible behavior of soils in geotechnical problems highlights the need for energy-conservative frameworks to simulate purely elastic responses. This study aims to develop a new hyperelastic model enriched by incorporating the coupling between plastic strains and elastic properties. Elastoplastic coupling aims to capture the evolution of elastic moduli caused by the anisotropy induced through variations in applied stress, which is associated with the history of previous shear loadings. The hyperelastic model is also implemented within a bounding surface plasticity framework for further assessment. Overall, the model's predictions show strong agreement with experimental data from several low-amplitude undrained unloading/reloading cycles during a drained test.