WARNING: The following contains spoilers for One Piece Chapter 1043, "Let's Face Death Together!!" by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English from Viz Media.
Luffy's Gear Fourth technique has proved to be among the most effective tools in his arsenal in One Piece. Not only does it give him a needed edge in tougher fights, but it has helped him to stand up to opponents who would normally have him outmatched. Even the Emperors of the Sea need to be careful when confronting Luffy in this form.
For how special Gear Fourth is, it doesn't come out very often. Luffy never even found an occasion to use the technique until he was well into his New World travels. Furthermore, it leaves him severely weakened after each use, so it's generally saved as a last resort. That's fine, as it adds to the spectacle when the technique finally makes an appearance. With that in mind, here's everything there is to know about Gear Fourth and when it appears throughout One Piece canon thus far.
What Is The Gear Fourth Technique in One Piece?
By blowing air into his muscles, Luffy grows into a hulking, top-heavy mass. He also coats his body in Armament Haki and emits steam in a distinct pattern around himself. This form grants him enhanced strength, speed and defensive capabilities all at once; that makes Gear Fourth a step up from both the speedy-but-weak Gear Second and the strong-but-slow Gear Third.
There have been three variations of Gear Fourth shown so far: Boundman, Tankman and Snakeman. The most commonly seen, Bound Man allows Luffy to use powerful, compression-based attacks. The punches he lands in this form are easily his most devastating.
Tank Man seems more focused on defense than offense, and is good for absorbing enemy blows. It can also take in opponents and launch them like a cannonball. So far, only the bloated "Manpuku Version" of this form has been seen.
Snake Man is the speed-oriented version of this form. By sacrificing offense and defense, Luffy is able to fire punches so fast that not even veteran fighters can properly dodge or block them. It might not be as tough as Boundman, but it's still formidable.
As powerful as Gear Fourth is, Luffy can't use it all the time. The technique drains him of both his stamina and his Haki. As such, he can only pull it out when he's certain he can win with it.
When Did Luffy Use Gear Fourth?
Luffy developed Gear Fourth during his two-year training session on Rusukaina. It was initially necessary to confront the giant animals that inhabited the island. It has since become one of Luffy's most reliable techniques for particularly difficult fights.
Gear Fourth debuted in Chapter 784, "Gear Fourth," when Luffy used its Boundman state against Doflamingo on Dressrossa. The former Warlord was powerless against the form on all fronts: offense, defense and speed. However, it still took Luffy a couple of tries to actually put down Doflamingo and keep him down.
In Chapter 837, "Luffy vs. Commander Cracker," Boundman was used again in the fight with Charlotte Cracker and his army of biscuit soldiers. When this didn't work, Luffy instead resorted to eating the soldiers. Then, in Chapter 842, "The Power of a Full Stomach," he used his Tankman "Manpuku Version (full stomach version)" to finish off the Sweet Commander. Despite how cartoonishly bloated eating all those biscuits made him, Gear Fourth caused him to metabolize it all within minutes.
Luffy later used another quickie Boundman in Chapter 871, "You Can Do It, Caesar!!" He was supposed to be running from Big Mom but had to go back for one good punch when she called him a coward. Unfortunately, the Emperor deflected his punch with her superior Armament Haki.
Luffy used Gear Fourth twice more against Charlotte Katakuri. First, in Chapter 884, "Who," he used Boundman against him while he was tilted from having his face revealed. Later, in Chapter 895, "Pirate Luffy vs. Commander Katakuri," he used Snakeman to keep up with his opponent's future-seeing Observation Haki and finally beat him. Many still argue about whether Katakuri let Luffy win, but having Gear Fourth most likely helped.
In Chapter 923, "Emperor of the Sea Kaidō vs. Luffy," the Straw Hat captain used Boundman in Wano on the drunk Beast Pirate Captain. Unfortunately, this did virtually no damage to Kaidō, and Luffy was quickly subdued. Luffy was later seen practicing Armament Haki emission in tandem with Gear Fourth in Chapter 955, "Enma."
Luffy used Boundman again to destroy a Beast Pirate ship in Chapter 975, "Kin'emon's Clever Trick." This instance is notable for not draining his stamina. Whether that's to become the norm is still unknown.
Luffy also needed Gear Fourth for the raid on Onigashima. He used it to help take down one of the Numbers in Chapter 990, "Army of One." He might have needed it against Ulti if Yamato hadn't intervened in Chapter 983, "Thunder."
Finally, Luffy used Gear Fourth twice more against Kaidō. The first time was in Chapter 1001, "Battle of Monsters on Onigashima." The second time was in Chapter 1041, "Komurasaki." Thanks to his training, he was able to do damage this time. It looked like he could have won, but he got distracted and Kaidō secured the win. To end on a positive note, this loss seems to be the prelude for a new ability courtesy of Joy Boy.