Chapter 612 is titled "Brought by the Shark They Saved".
In a brief flashback, three mermaids struggle to find out what is inside the Straw Hat's barrel, unaware it contains Caribou. They manage to open just enough of the barrel for Caribou to escape. The mermaids try to flee to the water, but it is no use. Caribou is able to capture them with the powers of the Numa Numa no Mi.
The Straw Hats arrive at Ryugu Palace, where King Neptune is scolded for leaving the palace unguarded. Luffy sneaks off when he smells food. He comes to a large iron door that he mistakes for the banquet hall. Inside, instead, he accidentally meets the Mermaid Princess, Shirahoshi.
The chapter begins by going back to Mermaid Cove a few hours prior to the present storyline. Ishilly is prying off the metal holds off of Caribou's barrel with a crowbar, wondering what is inside it. She thinks the barrels are sealed so tightly because it contains high-end expensive alcohol. She gets some of the holds off, which is enough to allow Caribou to break out. As Caribou breaks out, he thanks the mermaids. The terrified mermaids scream and Caribou tells them not to go anywhere. Ishilly yells for everyone to get into the water, but Caribou says that it is too late and turns his midsection into his Logia form, thanking Ishilly for freeing him once more. One mermaid yells out that her body is sinking, while another one realizes it is a swamp and asks why there is a swamp in the middle of the rocks. Caribou says that they are in a bottomless bog that is impossible to escape from. He tells them he is a "swamp man" who ate the Numa Numa no Mi. He then tells them that struggling will cause them to sink more and that they shouldn't scream or worry as he will not kill them. Ishilly tries to call for help but Caribou covers her mouth with one of his hands in swamp form, calling her naughty for not doing as she was told. Another mermaid calls out for Ishilly, but Caribou does the same to her, telling her she has to "go sleepy-bye" for a bit. The last things seen above the swamp are the sinking hands of one of the mermaids. Caribou then reverts back to his human form, talking about how his body is infinite and forgetting how much mermaids cost. He remembers that at the Human Auctioning House, they would sell for about 70,000,000 each and gets excited when he realizes how much he could get with three of them. He then realizes that he owes all of this to the Straw Hat Pirates. Their illegal entry made it so that he would not have to be subjected to any kind of immigration examination. He is now free to hunt as many mermaids as he wants, calling it a "treasure island", and then laughs happily.
Back to the present, in Coral Hill, a lot of people have gathered outside the Mermaid Cafe. The Straw Hat Pirates are believed to be behind the kidnappings at Mermaid Cove. Hiramera tells the crowd that she never explicitly stated that they were the culprits and that they were nice people and friends of Camie's. A voice in the crowd suggests they were threatened. The crew's wanted posters are spread out, with an Ammo Knight saying the only truth they know is the only people at the cove other than the mermaids were the Ammo Knights, the defeated New Fish-Man Pirates, and the Straw Hats. Another knight adds that humans always have a reason for kidnapping mermaids, mentioning their high value on the slave market. A man says that they cannot suspect the Straw Hats exclusively like that. Another knight asks him if he has any idea how many pirates look innocent to get close to mermaids and then kidnap them. Meanwhile, Fukaboshi asks Madam Shyarly if she really did have a vision of Luffy destroying Fish-Man Island. A mermaid brings her a cup of water. Having calmed down, she tells Fukaboshi that her vision was the truth. Fukaboshi tells Shyarly that the accuracy of her predictions is even apparent to those who live in Ryugu Palace. This complicates their plans to get in contact with the Straw Hats as they were indebted to them for saving their sister's pet, but due to the prediction the pirates cannot be left at large, and they must "deal" with the pirates now.
Over in Gyoverly Hills, residents are still looking up at the sky in awe as the Straw Hats ascend with King Neptune to the Ryugu Palace. The Straw Hats, Camie, and Pappag ride on Megalo while Neptune rides on Hoe as he calls to them not to fall off. Luffy asks why that old guy is shouting so loudly. Pappag is appalled and tells Luffy to be more respectful and Pappag is now frightened of Luffy. Neptune explains that Megalo is his daughter's beloved pet. She could not stop crying over how Megalo had not come home, that Neptune did not 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. Pappag thinks about the Mermaid Princess and Brook asks him if he was right in remembering that Pappag was once best friends with the princess. Pappag gives him a long "ssshhh" and Brook realizes it was a lie. Camie asks Usopp if he was sure it was ok for her and Pappag to go to the palace too. Usopp says that Neptune told them to bring their company, so it was fine. Neptune tells them that he had sent his sons out to get them, but when they did not 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 would not listen when Neptune suggested it would be more fun for everyone to drink together. Usopp asks if it was Zoro. Nami states it was Zoro. King Neptune then 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. Luffy asks Nami if she knew where the others went. Nami told them that Franky went to look for one of Tom's relatives and Robin went to look up some important history, so the three split up. She tells them that they did not really have too many problems. Nami then asks Neptune a question, calling him grandpa, causing Pappag to comically bite her on the head and tell her to call him god of the sea, Master Neptune. She asks why Fish-Man Island is so bright despite being 10,000 meters below the surface. Neptune tells her that Fish-Man Island came to be when fish-men began living on the sea floor where there was light. He explained that the roots from a tree called Sunlight Tree Eve reach down to the sea floor and transfer light to Fish-Man Island. Scholars have come up with a scientific reason behind how it works, but it is still considered a mysterious, sacred tree whose roots emit the light it absorbs from the surface. The roots also supply air to the ocean floor by breathing. Usopp considers it like the boss of the Yarukiman Mangroves at Sabaody. When the sun is out, there will be light on Fish-Man Island, which means it will also be dark at night. Neptune considers the sun a blessing that many take for granted. Usopp takes notes about it to tell Franky later as the Sunlight Tree Eve could have a connection to the Treasure Tree Adam. Nami says the tree's name while being lost in thought. Luffy tells Neptune he is hungry, calling him grandpa again, much to Pappag's annoyance as they approach the entrance to the palace, the outside of a giant, dark bubble. Neptune rings a doorbell, saying it is him. A stammering voice says they will open the gate at once. Once they were in the corridor beyond the gate, Neptune says "let's go", in excitement, shouting his own name as a battle cry. He calls to Megalo to keep the bubble tight. Luffy says that he is excited to see the palace.
Upon arriving at the palace, everyone looks at it in awe. Luffy thinks that it looks cool. Brook says it made Pappag's mansion look like a flea, prompting the starfish to tell him not to compare them. Nami marvels at its beauty. Camie chatters her teeth while being speechless. Voices are heard saying that the king has returned. 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 watch this scene, realizing the king is getting yelled at and told off like a child. Luffy, on the other hand, has caught the aroma of something pleasant. 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 that they did not 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. As they go on to tell him, the scene switches back to the Straw Hats. Nami wonders where Luffy went. Brook wonders when the banquet would start. Usopp says that Luffy was with them just a minute ago and that he cannot hold still. Pappag wonders in horror what Luffy could be doing wandering around the sacred land.
Luffy has followed his nose but lost the scent. He sees a door that he thought the smell of the food originated from. The double door in question was huge, made of mostly metal, and had two sets of handles, ring knockers high above and then regular handles near ground level. Embedded in the doors were three swords and a double-bladed axe. Embedded in the wall around the doorway was an axe, another sword, and the head of a morning star. Luffy, completely ignoring the weapons embedded in the doors and walls, walks over to the door. He says the sturdy look of the walls reminds him of Impel Down. He wonders how good the food behind that sturdy door could be. When he goes through the door, it is pitch black, but Luffy sees food on the other side of the room, making him wonder if the room was the banquet hall. He then wonders if he had found the food vault. Luffy then decides that he would only take a little bit of the food, as his stomach was at its limit. While running across the room, he crashes into something. He thought it was coral that felt really soft. When he first touches the coral, he hears a grunt, but thought it was someone outside. He then began jumping on the coral, comparing its consistency to pudding. He then hears someone ask if someone was in the room. A light suddenly came on and Luffy suddenly begins to fall. He falls next to a gargantuan giant smelt-whiting mermaid, the Mermaid Princess, Shirahoshi. What he had thought was coral was actually the coarse material of her top and the softness he felt was actually her breast. She asks him what he was doing on someone else's body and who he was. Luffy is amazed by the size of the princess. She then asks him if he was here to take her life too, and that she was not scared. She tries to hide her fear by saying she is the daughter of Neptune. But, she could not hold back her tears, which were so big that Luffy had to actually dodge the falling water droplets. She then yells for her father and brothers to help her, as Luffy pointed out that he wasn't doing anything to her.
- Caribou's Logia-type Devil Fruit is identified as the Numa Numa no Mi.
- After Caribou kidnapped Ishilly, and having heard Shyarly's prediction, Fukaboshi begins taking precautions against Luffy.
- Octopako, first seen in "Hatchan's Sea Floor Stroll", appears as a background character in this chapter.
- Megalo is revealed to be Princess Shirahoshi's pet.
- It is revealed that Pappag's claim of being friends with the Mermaid Princess was a lie.
- The light from Fish-Man Island comes from the root of a tree called Sunlight Tree Eve, which catches sunlight and casts it to the bottom of the sea via its roots. This is why the locals settled in that area. Usopp believes it may have some sort of connection to the Treasure Tree Adam and intends to ask Franky about it.
- The statuses of the other Straw Hats are revealed.
- Zoro is at Ryugu Palace.
- Robin is researching history.
- Franky is searching for a relative of Tom's.
- King Neptune's two ministers are introduced. Minister of the Right is a seahorse merman while Minister of the Left is a catfish merman.
- The Mermaid Princess, Shirahoshi, is fully introduced.
- Luffy's 400,000,000 bounty is seen on a wanted poster for the first time.
- Similarly to the events of the Water 7 arc, the Straw Hats are wrongfully blamed for the chaos that has happened on Fish-Man Island.
- first introduction
- first appearance