  LiVO$_2$ is a model system of the valence bond solid (VBS) in $3d^2$
triangular lattice. The origin of the VBS formation has remained controversial.
We investigate the microscopic mechanism by elucidating the $d$ orbital
character via on-site $^{51}$V NMR measurements in a single crystal up to 550 K
across a structural transition temperature $T_c$. The Knight shift, $K$, and
nuclear quadrupole frequency, $\delta \nu$, show that the 3d orbital with local
trigonal symmetry are reconstructed into a $d_{yz}d_{zx}$ orbital order below
$T_c$. Together with the NMR spectra with three-fold rotational symmetry, we
confirm a vanadium trimerization with $d$-$d$ $\sigma$ bonds. The Knight shift
extracts the large Van-Vleck orbital susceptibility, $\chi^{\rm VV} = 3.6
\times 10^{-4}$, in a paramagnetic state above $T_c$, which is comparable to
the spin susceptibility. The results suggest that orbitally induced Peierls
transition in the proximity of the frustrated itinerant state is the dominant
driving force of the trimerization transition.
