The Rainbow Moray Eel Brothers are all giant eels who are different colors. They all wear white hats that have colored bands on them corresponding with the appropriate color of the eel.
One day, the Straw Hat Pirates decided to play music in an attempt to catch fish. The Rainbow Moray Eel Brothers, who are attracted to music, came during the middle of the pirates' performance. After they left, the pirates commented on how rare their sighting is. Luffy wished he could've eaten them and Nico Robin stated that they must taste very good. Robin's statement has yet to be confirmed.