Abstract: Numerical simulations of biaxial compression tests were conducted on granular specimens with different initial densities using the discrete element method. The meso-loops formed by contacting particles were identified as fundamental structure to analyze the characteristics of stress-bearing and transmission during shear. Based on average stress, meso-loops were divided into strong and weak structures, and their structural reorganization and stress response evolution were analyzed. Numerical results show that the strain hardening/softening and unique meso critical stress state are also observed for different loop types in granular assemblies with different densities under shearing. Strong loops tend to be oriented in the loading direction, forming elongated chains that dominate deviatoric stress transmission. In contrast, weak loops also orient in the loading direction but aggregate into blocky clusters that fill voids between strong chains, providing auxiliary support. Moreover, both strong and weak structures tend to reorganize into highly anisotropic high-order 6+-cycle units, with greater macroscopic stress levels corresponding to stronger contributions of structural anisotropy. At the critical state, granular assemblies with different initial densities evolve toward topologically identical configurations in terms of quantity, geometry, and mechanical levels, thereby supporting and transmitting a unique critical stress under the same confining pressure. This reveals the structural uniqueness of the critical state at the macroscopic scale.