I would show them the Jaya Arc. It's a short setup arc that begins with Robin joining the crew and the fresh dynamic she brings as a new member.
What Jaya offers: a ship falling out from the sky, the looming giant shadows of Skypieans, a lawless town setting that captures pirate vibes, Blackbeard's iconic quote, Bellamy getting one-shot, the Gorosei's introduction, the debuts of Doffy, Kuma, and Sengoku, their meeting with Mihawk joining and Lafitte crashing it, the BBP introduction, updated bounties for Luffy and Zoro, and it ends with the Straw Hats blasting upward toward Sky Island.
The ending leaves you wanting more.