The older brother of the Neptune Family princes of Ryuuguu Kingdom. He formed the Neptune Army along with his two younger brothers by his father order, the king, to capture Van der Decken IX, who has been harassing the family's youngest daughter, the Ningyo Princess. When the Straw Hat crew arrived at Gyojin Island, he came to meet them with his brothers Ryuboshi and Manboshi for giving them a message by Jinbe, however, the crew ended up escaping after thoughting that they would arrest for their illegal entry. Fukaboshi is a shark ningyo.

Manboshi is a moonfish ningyo, one of the princes of the Ryuuguu Kingdom, the youngest of three brothers. He formed the Neptune Army along with his two younger brothers by his father order, the king, to capture Van der Decken IX, who has been harassing the family's youngest daughter, the Ningyo Princess. Manboshi is usually dancing and whistling shouting "Akkamanbo" all the time, that's because after the death of Queen Otohime, both his brother Ryuboshi and him try this way to show Shirahoshi that they are happy so she doesn't cry.

King of the Ryuuguu Kingdom located on Gyojin Island. Also known as the "God of the Sea", Neptune is a coelacanth ningyo. Driven by his deceased wife, Queen Otohime, Neptune has always had an approaching policy of his people towards the humans, it's even said that he had a close friendship with Shirohige, who had taken Gyojin Island as his protectorate.

The former Queen of Ryuuguu Kingdom. Otohime is a goldfish ningyo. Known for her struggle to promote the friendship of his people with the humans, Otohime collected signatures for years so Gyojin Island could be represented at the Levely. She even helped Mjosgard, a Tenryuubito who wrecked to Gyojin Island. Thanks to this event, Otohime encouraged to accompany the Tenryuubito to the surface to deal with the World Nobles, with which she achieved a recommendation letter. This event caused the increase of the number of signatures, raising the hopes of the island. However, one day someone set fire to the basket that contained the signatures, when Otohime arrived at the scene, someone shot her ending with her life. A human pirate was acused of the murder, but later it was revealed the authorship of Hody Jones. The morale of people fell again, but the three princes took up Otohime's dream continued collecting signatures.

Ryuboshi is a oarfish ningyo, one of the princes of the Ryuuguu Kingdom, the middle of three brothers. He formed the Neptune Army along with his two younger brothers by his father order, the king, to capture Van der Decken IX, who has been harassing the family's youngest daughter, the Ningyo Princess. Ryuboshi is usually singing all his sentences, that's because after the death of Queen Otohime, both his brother Manboshi and him try this way to show Shirahoshi that they are happy so she doesn't cry.

Minister of the left of the Ryuuguu Kingdom. He's a catfish ningyo.

Shirahoshi giant smelt-whiting ningyo. She is the famous Ningyo Princess, which is said to be the most beautiful woman in the world. Shirahoshi is the princess of the Ruyuuguu Kingdom of Fishman Island. She has been detained for years in the Hard Shell Tower of the Ryuuguu Palace due to Van der Decken's threat, a pirate who keeps threatening his life and says he wants to marry her. Although the true is that Van der Decken is after her legendary ability to control the Sea Kings.

Minister of the right of the Ryuuguu Kingdom. He's a seahorse ningyo.