From Pokémon.com In Pokémon Sun and Pokémon Moon, you can draw forth a Pokémon’s power to its utmost limit with Hyper Training. Pokémon grow stronger by raising their levels and increasing their base stats. However, their power is still affected by the individual strengths innate to each Pokémon. Now, with Hyper Training, Pokémon that have grown to Lv. 100 will be able to increase their individual strengths, which has never been possible before. With Hyper Training, you can increase the strength of the Lv. 100 Pokémon you've been adventuring with!