Hydride synthesis is an important technology in various fields represented by hydrogen storage and superconductivity . Among them, binary superhydrides with high hydrogen-to-metal (H/M) ratio were reported to have high Tc values . For example, Tc of LaH10 and CaH6 were 250-260 K at 180 GPa and 210 K at 160 GPa. It may be possible for room-temperature superconductors to be realized in ternary or quaternary hydride materials . Superhydrides are usually obtained by the close collaboration between theoretical simulations and experiments. Here, as an initial step, structure search methods such as metaheuristic methods and random search based on density functional theory (DFT) calculations have proposed novel structures. Subsequently, proposed superhydrides are realized by high-pressure synthesis using a diamond anvil cell (DAC). Although there might be a few exceptions, such as for LaH10 , hightemperature heating by laser irradiation is usually required to promote reactions. This implies that superhydride synthesis involves kinetically slow processes or reactions with high activation energies. Therefore, physical insights into the reactions are important to obtain efficient synthesis routes. However, measurements in microregions within DAC are limited to specific techniques such as white X-ray diffraction and Raman spectroscopy. In addition, since interfacial reactions involve large numbers of atoms, it is difficult to apply DFT calculations owing to large computational costs. Therefore, to the best of our knowledge, no studies have been carried out to directly analyze hydrogenation reaction dynamics, and the guidelines underpinning superhydride synthesis remain unclear.