Luffy, Usopp, and Chopper were going trick or treating and the others had to watch them to make sure they didn’t get into trouble. (luffy is obviously dressed up as a pirate, Nami is a princess, Zoro is Mihawk, Usopp is god, Sanji is a chef, Chopper is a ghost, robin is a demon, franky is a robot, and brook didn’t dress up.)