(The women of KNY are pirates and the men are mermen)

Koyuki passed out from swimming in the waters, Akaza the merman saved her but he was too far from shore until he saw the butterfly pirates

The butterfly pirates agreed to help him and he used a temporary spell to make himself human as a disguise

One day, Koyuki woke up and Akaza visited the ship one last time before leaving them forever

Hakuji(Akaza): gives Shinobu a chest of gold “here, as a thanks for helping Koyuki.”