Rechargeable batteries are encountering ever−growing demands for further improvements in energy density and safety. All−solid−state lithium−sulfur (Li−S) batteries have the potential to meet these demands, because they employ not only high−energy−density electrodes but also non−flammable inorganic solid electrolytes. However, the sluggish conducting nature of the S cathode results in high electric transfer barriers, making high S content in solid−state cathode composites difficult. In this study, we report the fabrication and reaction behavior of high S content cathode composites using a Li(CB9H10)0.7(CB11H12)0.3 superionic conductor. The lithium superionic conduction, high deformability, and low material density of Li(CB9H10)0.7(CB11H12)0.3 solid electrolyte facilitate intimate and favorable connections with sulfur and carbon, leading to facile electrical migrations within sulfur−Li(CB9H10)0.7(CB11H12)0.3−carbon (S−CH−C) composites. In battery tests, these close interconnections enable the fabrication of S−CH−C cathode composites through simple physical hand−mixing, allowing for reversible discharge−charge cycling of all−solid−state Li−S batteries engaging high energy density (>1,000 Wh kg−1cathode composite) S−CH−C cathode composites with a high S content of 50 wt%. In addition, a comparative investigation using various carbonaceous conductive materials suggests that simultaneously achieving high surface area, nanoparticle size, and non−spherical rough morphology is crucial for developing high S content S−CH−C composites with superior battery performances.