Cooperation between single-molecule magnets and electrical conductivity holds promise for preparing high-density magnetic devices; however, there are only a few reports so far. Here we report a 4f-π-based molecular hybrid, k-(ET)5Dy(NCS)7(KCl)0.5 (1) (ET = bis(ethylenedithio)tetrathiafulvalene, NCS- = thiocyanate), which undergoes slow relaxation of the magnetization and electrical conductivity. Unlike common ET-based conductive salts, K+ ions were intercalated into ET layers and coordinated with ET radicals. We found that the ET charges were sensitive to temperature, resulting in rich conductive phases at 75-300 K. In particular, the upturn in conductivity with a clear hysteresis loop was explained by the formation of partially oxidized states with charges close to 0.5+, which accounts for a metallic state. From the results of electronic structure calculations, the hole concentration increased to 125 K, which is consistent with a partially oxidized state upon cooling. The weak antiferromagnetic interactions accompanied by a dual magnetic relaxation process below 4 K are closely associated with the weak 4f-π interactions.