A crowdion is an interstitial atom embedded in a close-packed atomic row of a crystal lattice, it is very mobile and efficient in transferring energy and mass during plastic deformation, ion implantation, irradiation and other high-energy influences. Recently it was shown that the supersonic motion of an interstitial atom can be realized either by classical crowdion, or by a 2-crowdion, when not one, but two atoms have a high speed simultaneously. Usually static crowdions are studied using the ab initio approach, and moving excitations are modeled by the molecular dynamics method. This work presents a pioneering ab initio study of a supersonic 2-crowdion. The evolution of the electron density distribution during the motion of 2-crowdions with different supersonic speeds is analyzed. The results confirm a new mechanism of mass transfer by supersonic 2-crowdions.