Coordination Number: Early studies found that the conditions that are responsible for high ionic conductivity are realized with monovalent cation in a four-(tetrahedral) or three-coordinated configuration with the anions . Recent studies have expanded this idea to link the high ionic conductivity observed in lithium sulfides (e.g., LGPS and Li 7 P 3 S 11 ) to body-centered cubic (bcc) sulfur-sublattice, which can lead to energetically-equivalent tetrahedral (four-coordinated) sites of lithium and large transport channels . Collective motion: Subsequent investigations have revealed that the collective transport of lithium ions can flatten the migration energy barrier, thereby facilitating rapid ion conduction in materials like LGPS, cubic LLZO, and LATP. In these materials, it has been observed that, on average, two to three Li-ions migrate simultaneously . For instance, Burbano et al. ]. An interesting feature of these ionic conductors is the so-called paddle-wheel effect characterized by a strong correlation between the translational motion of the cation and the rotational one of the cluster , as depicted in Fig. ). Under thermal excitation, non-spherical clusters can lead to a rotationally disordered phase, creating low-energy pathways for ionic migrations and greatly enhancing ionic conductivity . This is exemplified by the high Na-ion conductivity of 30 mS cm -1 of NaCB 9 H 10 as it enters a rotationally disordered phase at RT. Therefore, fully exploiting the rotational degrees of freedom and utilizing the paddle-wheel effect could be a viable way to achieve high cation conductions. However, other than NaCB 9 H 10 , most of the known cluster-containing ionic conductors can only exhibit a transition to the rotational disordered phase at high temperatures (higher than RT) . It has been found that an amorphous structure with low density and a relatively large volume to accommodate the cluster can support the paddle-wheel effect even at low temperatures (e.g., RT) . Anion Valencies: Yet, the rotational freedom of the clusters in such a system seems to be limited, as it is still not comparable to that of the high-temperature phase; for instance Li 2 B 12 H 12 . On the other hand, one notices that the high charge states of the clusters (e.g., '-3' of PS 3 - moment of inertia may hinder their rotations under thermal excitation. Therefore, a combination of light mono-anion clusters with a chemically/structurally accommodating lattice framework could be the key to achieve exceptional high conductors that enjoy great rotational degrees of freedom of the cluster at RT. Introducing Anharmonicity: Anharmonicity is the deviation of a system from being a harmonic oscillator, which means that the restoring force is not proportional to the displacement of the system (Fig.