I tried the Search button and it didn't seem there was any discussion about it, but the "Moon Twin" connection between Mohkadun and Halloween has been noted, correct?

Anyway, all I can think is that this means that when the gang eventually goes to Mohkadun (it has to happen), Bun-Bun will be with them.

Additionally, given the speculations regarding Oasis and Kusari being, themselves, connected to the moon twin (even if just symbolically), well, that probably means Bun-Bun's will have an opportunity to make good on his word.

Mysteries upon mysteries.