Turbulent drag reduction is critical for enhancing the performance of hypersonic vehicles. The velocity-temperature coupled control strategy demonstrates considerable potential for drag reduction in hypersonic turbulent boundary layers (TBLs). Nevertheless, the mechanistic interplay between coherent structure modulation and resultant drag reduction remains insufficiently understood. In this study, the Direct Numerical Simulation (DNS) method is employed to elucidate the drag reduction mechanism of velocity-temperature coupled slot blowing in hypersonic flat-plate TBLs under different wall temperature conditions. For the present parameter range, the global drag reduction rates reach 25.59%, 20.19%, and 18.28% for cold, adiabatic, and hot-wall cases, respectively. Turbulent statistical characteristics reveal that slot blowing achieves skin friction reduction primarily by suppressing near-wall ejection events (Q2: ) and sweep events (Q4: ), which is associated with a contraction in the scale of coherent structures. In addition to conventional turbulence statistics, the clustering method is employed to identify coherent structures associated with Reynolds stress transport (Q2/Q4) and heat flux transport (Q2H: , Q4H: ), enabling a quantitative assessment of their respective contributions to the total skin friction. Combined with the FIK-like (Fukagata, Iwamoto and Kasagi) conditional skin friction decomposition, a plausible mechanistic explanation for the correlation between vortex dynamics and skin friction coefficients is proposed. The streamwise vortex scale is reduced by slot blowing, which weakens the occurrence of Q2 and Q4 events through the near-wall self-sustaining mechanism and consequently leads to a reduction in the wall-normal gradient of streamwise velocity ( ). This reduction, combined with ordered momentum injection by blowing, jointly contributes to the decrease in the wall-normal convection component (cf,My), which in turn contributes to drag reduction for both Q2/Q4 and Q2H/Q4H events.