Chapter 602 is titled "Rudder Straight Down!!"
"Usopp and Otters Have a Swimming Race in a River" - requested by pen name "President of Tea Ceremony Club (茶道部長)".
The Straw Hat Pirates finally set sail for Fishman Island. As they escape the Marines, they are seen off by the ones that helped them reach Sabaody. Many of them help the Straw Hat Pirates by stalling the Marines.
The chapter starts with Luffy saying goodbye to Rayleigh and thanking him once again while a voice off-screen yells "Capture Straw Hat!" There is a brief flashback of two instances during Luffy's training, Rayleigh then tells Luffy to aim for the top. Luffy, Zoro, and Sanji leave just as the Marines arrive. Rayleigh draws his sword, asking the Marines to respect the departure of his pupil. He then draws a line in the dirt with his sword's blade, saying that it would be a bad idea to cross the line. Elsewhere, while picking up Sanji's grocery, the Monster Trio is surrounded by more Marines. Suddenly, a Negative Hollow appears. Perona then appears, seemingly annoyed at the disturbance they were causing, asking what they were still doing there and why they had not left yet. The Marines behind her are suffering the effects of her Negative Hollow. Sanji (and obviously Zoro) recognize her, while Luffy does not. Perona then chastises Zoro for sounding ungrateful, reminding him that if it had not been for her, Zoro would not have reached the archipelago. She then tells them to hurry up since Marine vessels were right next to island.
Meanwhile, at Thousand Sunny, the crew members who had already arrived are rejoicing in seeing each other again. Brook, for the first time in two years, asks Nami if he could see her panties. Before he could finish his question, Nami promptly kicked him in the head, sending him flying into the wall. Nami then states that no one had matured during the two years they were separated. Chopper had gone to look for the others. Then, Luffy, Zoro, Sanji, and Chopper all arrived on one of the giant birds from Torino Kingdom. Everyone is overjoyed to see the last three crew members. Sanji, upon seeing Nami and Robin for the first time in two years, breaks out in a nosebleed so massive that the pressure from the gushing blood seemingly launches him from the bird. Once on the ship, Usopp tells Chopper to stop Sanji's bleeding. Luffy cannot help but marvel at Franky's new modifications. Nami tries to pull him out of this trance, saying they have bigger problems.
Suddenly, Thousand Sunny is bombarded by cannon fire. A Marine ship was already in range of the Straw Hat Pirates. The second round of cannon balls is stopped by Boa Hancock's Slave Arrows. The Kuja Pirates' ship intercepts the Marine ship, stalling their attack on the pirates. Robin identifies the ship as belonging to the Kuja. Usopp is shocked by Boa Hancock's presence and comments on her beauty. Sanji momentarily "turns to stone" from seeing her and Brook becomes mesmerized by her appearance. Usopp wonders why a Shichibukai would be at the archipelago before Luffy reveals that he knows her, much to their surprise. Hancock winks at Luffy. Brook sees this, causing him to fall over in shock. Nami asks Luffy how he knew her as Luffy explains that he met her on the Isle of Women. Usopp is surprised by the fact that such an island actually exists. Sanji yells at Luffy out of jealousy with tears in his eyes. Marguerite and Sweet Pea comment on the appearance of Luffy's crew, saying they looked fun and that there were types of people they had never seen before.
Franky then states that he will open valves so that air can flow in from the sack under the ship. The ship's coating starts to expand, forming a giant bubble around the ship, covering the deck with a bubble roof. Chopper then notices Usopp looking out at the archipelago and asks him if something is wrong. Usopp asks if all the Marines had been defeated. Chopper says that he did not think so. Usopp then comments that no one was chasing them. No one else seemed bothered by this, some even calling it luck. It is soon revealed why no Marines are following them.
The scene changes to the Marine's third backup platoon. They state that they cannot pursue the Straw Hats because giant insects, under the command of Heracles, were blocking their path. Heracles then wishes Usopp a safe journey. This happened to all the other Marine platoons. The fourth platoon's gunpowder was ruined by a sudden rain, that was isolated to only their location. It is revealed that the rain came from Weatheria, which was floating right above Sabaody Archipelago. Haredas and the other scientist were creating more diversions so that the crew could set off safely. Haredas then says that it will be lonely in Weatheria without Nami. The fifth platoon reported that the second platoon had gone completely negative, being held off by Perona. They also reported that the pirates escaped on a giant bird, which confused the person talking. Another platoon was intercepted by the okamas, claiming their hearts were about to be crushed; this affected Sanji too. One of the okamas said that now was Sanji's chance to escape.
Back at the Sunny, Nami started to explain how coated ships work. They have the ability to reduce various pressures, meaning that the ship cannot stay buoyant. The air sack is the only thing keeping the ship afloat at the moment. Both Luffy and Zoro simultaneously said that they did not understand. Franky resurfaces, saying that he had removed the air sack. Nami ordered everyone to raise the sails while they submerge. This confused Usopp, who thought that the ship would move on its own once underwater. Robin explains that underwater, ocean currents act as the equivalent of wind, thus, the currents move the ship. Luffy asked Nami if they were ready to go, to which she replies yes. Luffy then shouts that he has a lot of things to tell them, but for the moment wanted to thank them for putting up with his selfishness for the last two years. Usopp and Sanji sarcastically ask if he thought that was anything new, saying Luffy had always been like that. A Marine shouts to his commanding officer, a Rear Admiral, that the Straw Hats were escaping underwater, saying so while only the very top of the mast was still visible. The Rear Admiral, as well as the rest of the Marines, were being held captive by Boa Hancock's beauty. Luffy then yells "SET SAIL!" The chapter ends with the crew underwater, heading toward Fishman Island.
- Perona reappears and reveals that she brought Zoro to Sabaody.
- Hancock, Rayleigh, Heracles, the whole island of Weatheria (literally), Perona, the Okamas, and one of the giant birds from Torino Kingdom all aid the Straw Hats in escaping from the Marines. Only the revolutionaries and the citizens from the island of Karakuri Island did not show up, leaving Nico Robin and Franky the only Straw Hats who did not have a representative from where they went help the Straw Hats in Sabaody. Brook's managers only helped Brook return to Sabaody Archipelago but did nothing to aid the Straw Hats' escape.
- Luffy's crew sees Boa Hancock for the first time.
- Nami explains how a coated ship works.
- For the first time since their separation, the entire Straw Hat crew is seen together again.
- The Straw Hats are finally going to Fishman Island, which they have been planning to do since the end of the Post-Enies Lobby Arc, which was one hundred sixty seven chapters ago, and about 4 years in real time. The very first time Fishman Island was mentioned was in Arlong Park arc, around 12 years ago in real life time.
- Another Rear Admiral is introduced, the previous ones being the now pirate X Drake, an unnamed one from Impel Down, and the anime-only Yukimura.
- Sanji has his most severe nosebleed so far. So severe, in fact, that it was actually acknowledged by Usopp and the bleeding had to be treated by Chopper.
- Sanji not only fell in love with Hancock, he turned to stone without her doing anything.
- This is the last chapter of the Return to Sabaody Arc.
- The title, "Shimokaji Ippai!!", is a pun on 'omokaji ippai' which roughly means 'hard to starboard' (nautical term for 'to the right').