The nonpolar solvation dynamics in Lennard-Jones fluids is discussed in terms of the relationship with the dynamic structure factor of neat solvent, using the theoretical expression that describes the solvation correlation function as the superposition of solvent dynamic structure factors at various wavenumbers. Several expressions for the coupling strength between the state transition of the solute and the solvent density modes are examined with respect to their abilities to predict the static fluctuation. In the present theoretical model, it is found that the difference between the ground- and excited-state solute-solvent interactions can be adequately taken as the coupling strength with the solvent density mode. Employing this expression for the coupling, the solvent fluctuation around k congruent to sigma(-1) (sigma stands for the diameter of the solvent) contributes dominantly to the static fluctuation in all the densities investigated. This corresponds to the feature of the solvation dynamics in mixed solvents, in which the effective wavenumber is determined to be 1.14sigma(-1) from the proportionality between the solvation rates and the diffusion coefficients in the higher-density region. The half decay time (t(1/2)) of the dynamic structure factor at this wavenumber shows similar density dependence to that of the solvation correlation function obtained in our previous work. The half decay time of the dynamic structure factor is correlated with the static structure factor. This supports our previous proposal that the curvature of the free energy surface along the solvation coordinate is essential to the solvation dynamics. The agreement between the present theory and the simulation is further improved by taking the motion of the solute into account.