Neptune

King Neptune (ネプチューン王) is a coelacanth merman and the king of the Ryugu Kingdom on Fishman Island. He is the father of Fukaboshi, Ryuboshi, Manboshi, and Shirahoshi, and the husband of the late Queen Otohime.

Appearance
Neptune is a giant muscular coelacanth merman. He has a darkened nose and long thick curly hair and beard. He bears matching tattoos on both arms, and is bare-chested. As king, he wears a crown that resembles a tulip and carries a trident with an elaborate design.

Personality
Neptune seems to be very blunt, as he simply invited the "Straw Hat humans" to the Ryugu Palace, instead of being more cordial. He also tends to shout his words out for no reason, including a habit of shouting his own name at random times, being followed by his whale shouting "Hoe". Neptune sometimes mispronounces people's names, as he refers to Zoro as "Zori". He appears to be easy-going, absent minded, and carefree as he was scolded by his ministers for leaving the castle on a whim on more than one occasion.

However, he can be serious when the situation demands it, as he intended to capture the Straw Hat Pirates when they were wrongly accused of kidnapping mermaids, though Neptune did not think it was fair to arrest them based on a prediction made by Madame Shirley, and merely wanted to capture the crew rather than arrest them for a precaution.

He dotes on his only daughter Shirahoshi, and worries about her immensely. He provided several extreme but necessary security measures to protect her from Vander Decken IX, and even attempted to beg the Straw Hats to rush to her aid when he thought that his daughter is in danger. Neptune apparently acknowledges the value of sacrifice, as he decided that he would rather risk his daughter's safety in the hands of strangers than in Decken's captivity. He gets quite upset when he hears that Shirahoshi is upset and very emotional when she is in danger.

Neptune is also partially perceptive as he correctly guessed that Luffy snuck Shirahoshi out of Hard-Shell Tower by stuffing her inside Megalo, even though everyone else thought this was a bizarre idea. However, he can jump to conclusions when he stopped suspecting Luffy only after Vander Decken IX appeared in the palace and quickly accused Decken of kidnapping Shirahoshi.

Like many other characters in the series, he appears to have a unique laugh: Hoh hoh hoh hoh.

Family and Kingdom
Neptune appears to be very protective of his family, as he had his sons form an army solely to track down Vander Decken IX so that the pirate would stop harassing his daughter. He also has a beloved whale named Hoe. The Ministers of the Left and Right tend to yell at Neptune for his lack of responsibility as the king of Ryugu Kingdom, and he doesn't seem to have any resentment to that.

When he was tied up after his failed attempt to capture the Straw Hats, Neptune begged the pirates to ensure Shirahoshi's safety when he suspected that she might be in danger, showing great concern for his daughter, and warned the crew that if anything happened to Shirahoshi, he would hunt them down to the ends of the sea. Neptune considers Shirahoshi to be very precious to him as after Decken went after her. He begs the Straw Hats to stop Decken, going as far as to offer the crew anything.

As he is with his family, he also cares deeply about his subjects, going so far as to block an attack made by Hordy Jones against his soldiers while they were tied up, despite being wounded as a result.

Enemies
Since Vander Decken IX kept annoying Shirahoshi with threatening letters of marriage proposals, he has earned Neptune's wrath, leading him to form an army against the pirate.

Neptune's other enemy is Hordy Jones, a fishman who follows Arlong's ideals. Jones believes that Neptune is unfit to rule Fishman Island and intends to overthrow him.

Abilities and Powers
As the king, he has royal authority over the entire Ryugu Kingdom. His presence outside the palace is enough to cause a commotion with the citizens referring him as "You-Know-Who".

While he is the king of Fishman Island, he has had to rely on the protection of two of the Yonkou: Whitebeard until his death and then Charlotte Linlin (Big Mam) afterwards. He didn't have to pay collateral to Whitebeard, but he does have to pay a monthly fee of sweet candy to Big Mam.

He is known to be extremely powerful in combat, but his strength seems to have weakened due to having sprained his back and general old age, but he is still strong enough for the Straw Hat Pirates to require chains to tie him up as opposed to the normal ropes used on the guards. He is shown capable of manipulating water, grabbing it with his hands as if it were something solid, to perform extremely powerful, large-scale attacks.

Weapons
He carries around a gigantic trident fitting his size, and is presumably proficient in using it, as Brook and many fishmen acknowledged his strength. Zoro, however, seemingly stopped one of his attacks with ease, and soon after managed to subdue Neptune and lock him in chains without recieving any visible injuries, although, according to Neptune, he was taken by surprise.

Attacks

 * Merman Combat: Ultramarine (人魚柔術（マーマンコンバット） ウルトラマリン): Neptune grabs the water with his hands as if it were solid, similar to Jinbe's Mizugokoro, and then hurls it forward in a mighty, extremely large torrent that blasts away his opponents with great strength. "Ultramarine" usually refers to a shade of blue and got its name from "ultramarinus", literally meaning "beyond the sea". This was first used against the New Fishman Pirates, and Neptune suffered extreme pain from his strained back after this technique.

Past
He was so angered by Vander Decken IX pestering his daughter through letters, packages, and ultimately marriage proposals, that he had his three sons form an army called the Neptune Army to capture him.

When Shirahoshi's pet shark, Megalo, went missing (having been swallowed by the Kraken), Shirahoshi kept crying and crying and Neptune did not know what to do. Eventually, the shark returned to the palace.

Meeting the Straw Hats
When Megalo tells him about being freed by the Straw Hat Pirates, he looks forward to meeting them. When he learns that Straw Hat Luffy is in Pappug's mansion, he personally travels there to meet him. After making contact with Luffy, King Neptune invites him and his crew to his palace.

The Straw Hats, Keimi, and Pappug rides on Megalo while Neptune rides on Hoe as he calls to them not to fall off. Neptune explains that Megalo is his daughter's beloved pet. She could not stop crying over how Megalo had not come home that Neptune didn't know what to do with her. He thinks about how dangerous fighting the Kraken must have been and thanks them for their great work. Luffy tells him that it was just a coincidence but he was glad to help. Neptune tells them that he had sent his sons out to get them, but when they didn't come back, he went out himself.

He says that he was excited for the banquet's menu and wanted to start as soon as possible. He then remembers that one of the Straw Hats was already at the palace. He had already started drinking and wouldn't listen when Neptune suggested it would be more fun for everyone to drink together. King Neptune says that he thought his name was Zori, and gets corrected with the right name. Neptune goes on to tell them that his soldiers will find all of the other Straw Hats and bring them to the castle.

Nami then asks Neptune a question about why Fishman Island is so bright despite being 10,000 meters below the surface. Neptune tells her that Fishman Island came to be when fishmen began living on the sea floor where there was light. He explains that the roots from a tree called Sunlight Tree Eve reach down to the sea floor and transfer light to Fishman Island.

They approach the entrance of the palace. Neptune rings a doorbell, saying it is him, and a stammering voice says that they will open the gate at once. Once they are in the corridor beyond the gate, Neptune said "let's go", in excitement, shouting his own name as a battle cry. Luffy says that it looked like a cool palace with a lot of stuff. Neptune answers him bluntly saying of course it would as it is his castle. He then tells everyone to enjoy themselves.

Once inside the castle, two men instantly start berating Neptune for going out on his own. He tells them he will be sure to be more careful in the future. Everyone but Luffy watches this scene, realizing the king is getting yelled at and told off like a child. Neptune tells the men that he brought the people who saved Megalo from the Kraken. He also asks where his daughter, Princess Shirahoshi, is. The men tell him that "it" happened again just a moment ago. Neptune gets angry, telling the men they didn't set her up with the proper guarding to keep her from getting upset. One of the men retorts that the king disappearing during such a critical time would get the whole castle upset. He then lowers his head, apologizing and promising to take better care next time. The Straw Hats realize he is getting yelled at again. The two men who were berating the king are the Minister of the Right, a seahorse merman, and the Minister of the Left, a catfish merman. The Minister of the Right apologizes for berating the king in front of his guests, but they have something important to discuss with him. The Minister of the Left tells them they received a message from Fukaboshi.

A Siege at the Palace
After receiving word of the mysterious disappearances of the mermaids from Mermaid Cove and of Madame Shirley's ominous prediction, the palace guards and personnel took action against the Straw Hats. After some of the guards are overwhelmed by Nami, Usopp, and Brook, The Minister of the Left begs Neptune to use his power against the pirates. Neptune doesn't wish to go against them just because of a prediction. He attempts to subdue the pirates, but Zoro intercepts him.

He is next seen chained up along with his ministers and the castle guards. He comments on how he has not been able to fight all that well after straining his back. He admits that he has gotten old and apologizes for being unprepared. Neptune's sons return, but they are stuck outside since the only way in the caste is the palace entrance. Zoro then speaks with Fukaboshi through Den Den Mushi while making some demands. Neptune informs Fukaboshi that he is speaking to the pirate who is now worth 160,000,000. Neptune is then surprised to hear a sound coming from Shirahoshi's tower.

He realizes his daughter is in danger and asks if there are guards posted by her room. He is then told that they are all tied up with him. He then orders the Straw Hat Pirates to go and make sure Shirahoshi is safe. When the guards protest, Neptune tells them that dire situations call for sacrifice. He then angrily tells the Straw Hats to go to the northeast part of the palace where the tower is located. When Zoro asks why they should take orders from a hostage, Neptune becomes even more angry, telling them that if anything happens to his daughter while he is incapacitated, he would chase the pirates to the ends of the ocean.

Brook and the Minister of the Right then go straight to Shirahoshi's room and find her missing, having already left with Luffy and Megalo. When they inform Neptune about this, the king looks stunned. He then starts crying out and demands that the Straw Hats return Shirahoshi. Usopp yells back saying that they didn't kidnap the princess. Brook points out that he only saw Luffy and Megalo leave Shirahoshi's room. Neptune correctly guessed that Shirahoshi has been stuffed into Megalo, even though everyone else thought his idea was preposterous. The palace guards laugh at this statement saying that it is way too bizarre.

When Hordy Jones and Vander Decken IX arrive at the palace, King Neptune quickly accuses Decken of kidnapping the princess. This makes Decken realize that Shirahoshi has left the palace and he quickly goes after her. Neptune then tearfully begs the Straw Hats to stop Decken, going as far as to offer them anything. Hordy Jones then crushes a palace wall, flooding the palace in the process. Jones then launches his Archer Shark attack. Neptune protects some of his soldiers by taking some of the hits. Zoro then cuts his chains, saying that their deal with the hostages was void since they got hurt. Before everyone is completely submerged under water, Usopp and Brook untie the palace guards and Zoro tells Neptune to take his crew mates to safety.

Neptune then tells his guards to allow Hordy Jones to take the palace. Neptune says that they need to regroup with Fukaboshi, so they can prepare for another battle with the New Fishman Pirates. After Zoro staggers Jones with one slash, Neptune takes Zoro, Usopp, and Brook and prepares an escape route. Neptune creates a vortex and clears a path. The ministers and the palace guards escape. However, Neptune's back gave in putting him, Zoro, Usopp, and Brook in a dangerous situation. Hoe arrives to save them, but Jones, energized by an Energy Steroid, stops Neptune with one hand. Neptune and the three Straw Hats with him are then captured by the New Fishman Pirates.

Major Battles

 * Neptune and Ryugu Palace guards vs. Roronoa Zoro, Nami, Usopp, and Brook
 * Neptune vs. New Fishman Pirates

Trivia

 * His name comes from Neptune, the Roman god of the sea.
 * His appearance (wild hair and beard, broad build, trident, etc.) is a common depiction of mermen in popular culture, particularly sea gods and rulers such as Triton from Disney's "The Little Mermaid".
 * He is a coelacanth merman, the significance of this being that the Indonesian species is referred to locally as "Raja laut", meaning "King of the Sea".
 * His thick beard, friendliness, and "ho-ho-ho" laugh are hallmark features of Santa Claus.
 * His tail didn't split even if he is probably older than 30. It is unknown if he actually is younger, or it is a mistake of Oda, or his type of fishtail doesn't split at all. It is also possible that he simply chose to keep his split tail merged, like when Kokoro did to swim.