The Straw Hat Pirates split up in episode 405 of the anime and in chapter 513 of the One Piece manga.
In episode 405 of the One Piece anime titled “Disappearing Crew - The Final Day of the Straw Hat Crew”, the Straw Hats were utterly defeated at the hands of Warlord Kuma, the Tyrant. Kuma used his devil fruit prowess to send the Straw Hats flying, forcing the crew to split up.
|Episode Number||Episode 405|
|Episode Name||Disappearing Crew - The Final Day of the Straw Hat Crew|
|Manga Chapter||Chapter 513|
|Chapter Name||Beyond Rescue!!!|
Over the Sabaody Archipelago, a bubble pops, symbolizing Zoro's disappearance. Usopp yells out in despair, wanting to know what Kuma did to Zoro. Chopper, who is running amok in his monster form, slaps Luffy and Robin as Luffy cries in anguish. While Luffy cries out to Zoro, Robin tries to control Chopper as he is risking his life in his monster form and would eventually die if he doesn't calm down and return to his former self. Sentomaru avoids Chopper's vicious smash and asks him what he is doing in this location. Rayleigh and Kizaru are still engaged in combat. While Rayleigh is focused on his battle, the Kizaru is aware that the Shichibukai (Warlord of the Sea) are required to report to Marine Headquarters. As Nami had seen it earlier on Thriller Bark, Franky notices that Kuma had erased Zoro and wishes that Zoro is able to survive this and is still somehow alive.
Sentomaru, who claims that he is the World's Most Guarded Man, refuses to answer when Luffy asks him what happened to Zoro. Although he does acknowledge that when Kuma smacks someone with his paw pads, they will fly for three days and nights, he still believes this to be merely a legend. Zoro is no longer in the Sabaody Archipelago, but Kuma is the only one who knows where his victims end up. Meanwhile, a Pacifista aims as Usopp attempts to attack Kuma, but the warlord brushes the Pacifista away with his paw pad. Sentomaru starts chastising Kuma for attacking one of their own.
In an effort to find a means to change the course of events, Luffy orders his crew to completely retreat and acknowledges that they cannot win this fight as they are simply not strong enough to win at the time. Usopp tries to take Sanji to safety as Nami starts to run with Franky. Brook makes a commitment to sacrifice himself in order to save his friends, but Kuma just brushes him aside. Sanji loses his cool and tells Usopp to leave. He tries to stand, but the tyrant prevents him from fighting. Usopp tries to protect himself, but Kuma swats him off the island, just like he did with Zoro and Brook.
Sanji makes a last-ditch effort but is likewise defeated. Meanwhile, Rayleigh is still engaged in battle with Kizaru and his hands are full, unable to aid the Straw Hats anymore than he already is. Rayleigh is then confronted by Kuma, who asks him to trust him. Luffy shifts into Second Gear in an attempt to save his friends but Kuma easily deflects his attack. Kuma then appears before Nami and Franky and deflects Franky's attack. Kuma swats Franky with his paw pad as he is still in disbelief about his captain's predicament. Nami begs in anguish for Luffy to help and save her, but Kuma's paw swipes her off the island, just like everyone before her.
Luffy becomes outraged following Nami's death and attempts to attack Kuma once again but misses. When Monster Chopper finds Kuma, he makes an attempt at a brave sacrifice, but like the rest of the crew, Kuma's paw chases him off the island. Luffy starts to lose hope and reaches out to Robin, but Kuma uses his paw pad to send her flying and vanishing before Luffy could reach her. As a result of his incompetence and failure to save his crew, Luffy starts to cry as he reminisces about his time with his beloved crew. Kizaru demands Kuma give an explanation for his behavior. The warlord informs Luffy that they won't ever cross paths again and bids him farewell before he sends him flying with his paw pad.
Straw Hats are defeated at the hands of Kuma, Warlord of the Sea.
The Straw Hat Crew splits up as a result of their defeat.
A. The Straw Hats get back together in episode 517 of the One Piece anime with the title, A New Chapter Begins - The Straw Hat Crew Reunites!
A. Although every single Straw Hat wanted to get back together with their crew, they realized that they needed to get stronger after the events of the Sabaody Archipelago. As per Luffy’s order, they all decided to reunite after 2 years and they used these 2 years to expand their horizons and prepare themselves for the New World.