Episode 7

In episode 7 of the seventeenth season (XY series),' Giving Chase at the Rhyhorn Race!; it is also revealed that at some point in his childhood, Ash had attended a Pokemon Summer Camp, where he had previously met childhood friend Serena. At one point during the camp, Serena had hurt her knee from falling over after being startled by a Poliwag. Ash had used his hankerchief to wrap up her injury, which she had kept, and returns to Ash in this episode. https://www.youtube.com/watch?v=z8BcZ0nCmxA: