Elysia is Gladion and Lillie's adopted sister, though they both cared for her a lot because she was very soft, kind and tough when she needs to be especially strong in Pokémon battles. She always understood Gladion's reasons for wanting to save Alola from total destruction which was the only condition she agreed to travel with him, which he reluctantly agreed to. Both were in a cave after it started raining to shelter from it.

"You should take your pokemon out for air, I'll do the same. Since we're going to be here for a while until it stops raining."

Gladion mentioned. Even if he came across as rough and cold on the outside, Elysia knew he was someone who cared about his loved ones...especially her, Lillie, his mother and his father.