Pokémon the Series: Sun & Moon Episode 27: A Glaring Rivalry!
Episode 27 of 146 of Pokémon the Series: Sun & Moon, aired May 18, 2017, 25 minutes. Available with English subtitles and dub where released.
Episode summary
When Lillie’s big brother Gladion arrives on Melemele Island, everyone is excited about the powerful new Trainer in town—particularly Ash, who really wants to battle him! After hearing about Ash’s Z-Ring and his battles against Tapu Koko, Gladion agrees to meet up the next morning.