Walkthrough: After defeating Gladion at the base of Mount Lanakila, you will discover that Lillie is back with Solgaleo in Mahalo Trail on Melemele Island. Before challenging the Pokemon League, you can actually head back there to find the two of them. As you reach them, Lillie will explain how she thinks Solgaleo and Necrozma should be together once again, citing how Solgaleo can help Necrozma. She will then ask you to capture Solgaleo, as she believes only you are strong enough to make such a thing happen. Solgaleo will be at Level 60, knowing the moves of Sunsteel Strike, Cosmic Power, Crunch, and Zen Headbutt.