Usopp's the Strongest? Leave Anything Negative to Him

Luffy continues on to take on Moria while Chopper and Robin remain behind to take on Hogback who sics Jigoro and Inuppe on them. After Oars runs off with a new pirate hat from his destruction, his actions disrupting Abalsom as his wedding to Nami is almost complete, the remainder of the crew end up in Perona's room where she uses her negative powers on them. But Usopp reveals that he's immune to her attacks due his negative personality, staying behind to take on the ghost princess while the others continue towards Absalom and Ryuuma.