The moon appears throughout the series, but the first time the moon was seen was when Zoro fought Kuina in his childhood flashback.[1] Later Kuro used the moon as a signal to carry out his three-year plan; the sight of a crescent moon makes him uncontrollably murderous.[2][3] During the sequences that influence Kuro, the moon was shown to be a red-orange crescent. In subsequent appearances the moon begins to be hard-sketched.
During Nico Robin's flashback of Ohara, a model of the world with seven satellites (which includes their world's moon) can be seen inside the library of the Tree of Knowledge.[4] The model was destroyed when the Buster Call attack caused the tree to collapse.
Traveling to the moon seems to be considerably easier than in real life, as Enel managed to go there using the Ark Maxim,[5] and the four automata managed to go there traveling in balloons.[6]