Chapter 618 is titled "Proposal".
The chapter starts with everyone exclaiming that the Mermaid Princess has been kidnapped. Luffy asks Shirahoshi why she got out of Megalo's mouth, she apologizes and asks him not to get mad at her as she starts to cry. As someone calls Luffy filthy and heartless, Chopper urges Sanji not to turn around. Sanji realizes that Chopper's warning can only mean that the Mermaid Princess is right behind him. Chopper tells him he is correct, but seeing the princess would without a doubt kill him if a normal mermaid made him lose so much blood before. As Sanji begins to get lost in thought, he remembers hearing that even the most beautiful woman in the world, the pirate empress, would pale in comparison, and realizes that his dream is now in his grasp. He then tells Chopper that for the sake of his dreams, he chooses death- Chopper retorts by exclaiming that he thought that his dream was to find the All Blue. He turns around and looks at her. He realizes that he is gazing upon something that his imagination could never fathom, that no painting could ever capture. He then turns to stone, much to Chopper's shock. Luffy is examining Hatchan, trying to get Hachi to tell him who attacked him. Chopper wonders if Sanji turning to stone could be from a side effect of receiving okama blood. Shirahoshi cries and asks Luffy what she should do, but all of a sudden the Locals take action and tie up Luffy, Chopper, Hatchan, and the still petrified Sanji. Luffy asks them what they are doing, and the locals tell him not to underestimate the warriors of Fishman Island. One of the locals identify Hatchan as a former member of Arlong's gang. Shirahoshi tries to explain to everyone that Luffy was only helping her, but the locals will not listen and promise to behead the pirates. Luffy then notices something and tells them that something is flying toward them from behind the crowd, but a local asks Luffy if he really thinks they are dumb enough to fall for that.
Someone then notices that Luffy is not lying, and everyone is shocked to see it is none other than Vander Decken IX. Decken yells that he found her, this time saying "Of course I did" instead of "I think". The locals are shocked that after hiding out for ten years, he now suddenly appeared on the island, and someone yells for Shirahoshi to run for it. Decken tells Shirahoshi to give him an answer, saying she will escape death if she says yes, telling her to run away with him and marry him. The locals are shocked to hear him ask for marriage after constantly attempting to take her life. Shirahoshi tells him she is sorry, but he is not her type. The locals are comically stunned to find out that is why she will not marry him, and not his violent tendencies. Decken is crushed, and actually looks emotionally hurt. He tells her she should be ashamed of herself, because he has had feelings for her for the past ten years and then she steps all over them. He then asks her who she is planning to be with. He goes on to say that now that he knows her feelings toward him, her existence is now an eyesore. He gets ready to attack her as a local tells her to run, but Luffy tells her to wait, having now dubbed her 'scaredy cat'. A local grabs him by the collar, and asks him if he is working for Decken, and if he wants the princess to die. Luffy shouts that if she gets too far away from him, then he cannot protect her, so Shirahoshi tells Luffy she will remain with him. Decken then attacks Shirahoshi with another axe with a rose painted on it. Luffy tries to help, but is blocked by locals who still think he is trying to harm the princess. Luffy apologizes, saying he has nothing against them, then knocks them out with a burst of Haoshoku Haki because they are in his way. He then kicks off from the ground, flying toward Decken who is still on the coral. He does a flip in the air and brings his legs down on the coral, sending it crashing to the ground and knocking Decken off. The locals are amazed at Luffy's abilities, even when he is tied up.
Decken asks Luffy why he is interfering with his and Shirahoshi's love, and figures that Luffy was the one who brought Shirahoshi out of the palace. And Luffy realizes that Decken was the one who had been throwing things at Shirahoshi as he gets ready to do an attack. Decken tells him he will take both of their lives, saying they would not be a pair, as they would be cut into a set of four. Luffy then uses a new technique, Gomu Gomu no Jet Hammer, plowing Vander Decken IX into the ground head first. The locals are shocked to see that Luffy beat Vander Decken. They then realize that Decken was still moving, despite being planted head first into the ground, and decide to capture him. Luffy headbutts Megalo, telling him to wake up and asks Sanji if he is alright. Chopper tells Luffy that Sanji had turned to stone earlier, but now he seems happy, and most importantly, conscious. Luffy tells Shirahoshi they need to go. Shirahoshi asks Luffy not to yell at her, as all the excitement has gotten her quite worked up. Luffy tells her that for some reason the island hates them, and they need to get out of here.
Shirahoshi unties Luffy, making the locals wonder why she is helping him. She apologizes to them, and tells them she will be home in time for dinner, which confuses them. The Straw Hats get on Megalo's back, and Shirahoshi grabs on to his jaws (much to his discomfort), as they get away. Just as they get away, Vander Decken IX gets his head out of the ground and swats away the people trying to capture him. Yelling that they will not get away, he calls on Wadatsumi and tells him to pound them into the ground. Wadatsumi gets ready to punch them, but Luffy beats him to it, and hits him in the face with a Gomu Gomu no Jet Pistol, breaking one of his teeth. Decken seems upset that they got away.
The scene changes to the Ryugu Palace, where someone informs Jones that Nami and Keimi had escaped. Jones tells him to ignore it. Nami and Keimi are then seen escaping, with the former holding onto the latter's back with an air bubble around her head. Keimi asks if it was ok for them to leave the others behind but Nami tells her to relax, as nothing good could come by worrying. Keimi tells her she knows that they are all strong, but that Hatchan told her that Jones's mind is more dangerous than his strength. Nami then asks her what kind of person Jinbe is. Keimi replies that he is a pirate who is popular at the Ryugu Palace and can come and go as he pleases. Nami remembers that he was also in the same crew as Arlong, and that Jones is the successor to Arlong's will. She then mentions one of Jinbe's messages to Luffy, "Don't fight Hody". Nami adds that she thinks she has figured out what the message means. Keimi tells her she thought it only meant that Jones is dangerous. Nami adds that it is ok for Zoro and the others to get Jones angry. She then tells Keimi she wants to meet Jinbe, and remembers he is waiting at the Sea Forest. Nami says that the situation seems to have a long and deep rooted history, and has a feeling that Jinbe knows all about it. She then asks Keimi to head to the sea forest.
Back in the palace, Neptune is giving orders to his guards. The soldiers tell him they will take care of Jones and the pirates. Neptune tells them not to. He tells them that even though he did not get a chance to fight, they all ended up as victims. He orders them to surrender the castle for now, reunite with Fukaboshi, and get ready for the rematch. The guards are shocked at the orders. Usopp and Brook are in the water. Usopp wonders what Zoro can do to fight a fishman in the water as Brook tells Usopp he is not going to make it. The chapter ends with Zoro seemingly defeating Jones with a single slash, and the New Fishman Pirates astounded at what happened to their captain, with Usopp looking on in shock.
- This is the second time Sanji has turned to stone, the first was when he saw Boa Hancock. Both women are considered the two most beautiful women in the world.
- Shirahoshi rejects Vander Decken IX's proposal, saying that he is not her type.
- Luffy gives Shirahoshi a new nickname, "Scaredy-Cat".
- Luffy, Sanji, Chopper, Hatchan, Nami, and Keimi are all heading for the Sea Forest. Counting Robin who is already heading there, that makes five Straw Hats heading to the Sea Forest with Franky already there.
- Neptune decides to allow the New Fishman Pirates to take over the palace, saying it is more important to escape and regroup with their forces.
- It is revealed that Jinbe is popular enough with the royal family that he can come and go from the palace as he pleases.
- Zoro deals a serious blow to Hody Jones with one slash.
- Pandaman appeared among the crowd on the page where Shirahoshi rejected Decken's proposal.