Big Fight under the Moon! The Pirate Flag Flutters with Sorrow! - S8.E235

Once they're back on the ship, Luffy has to finally tell Usopp that the Going Merry can no longer be repaired and that they've chosen to get a new ship without him. Usopp believes that Luffy has abandoned the dignity of their ship and says he's leaving the crew. That night, he challenges Luffy to a duel.