  We present a first study on a pair of triply charmed baryons,
$\Omega_{ccc}\Omega_{ccc}$ in the $^1S_0$ channel, on the basis of the HAL QCD
method. The measurements are perfomed on the $(2+1)$-flavor lattice QCD
configurations with nearly physical light-quark masses and physical charm-quark
mass. We show that the system with the Coulomb repulsion taking into account
the charge form factor of $\Omega_{ccc}$ leads to the scattering length
$a^\mathrm{C}_0\simeq-19$ fm and the effective range
$r^\mathrm{C}_\mathrm{eff}\simeq0.45$ fm, which indicates
$\Omega_{ccc}\Omega_{ccc}$ is located in the unitary regime.
