WARNING: The following contains spoilers for One Piece, Chapter #1,000 by Eiichiro Oda, Stephen Paul, and Vanessa Satone, available in English now from Viz Media.
In the long-anticipated Chapter #1,000 of One Piece, when Luffy finally reaches the rooftop of Onigashima where Kaido is waiting for him, the rubber man pays no mind to the Yonko. Instead, he tends right away to the injured Kin'emon and the other Scabbards, until Trafalgar teleports them out of danger. Outraged by the lack of respect, Kaido gets ready to crush Luffy with his club, but the rubber man evades him; instead, returning fire with a brand new attack, known as Gum-Gum Red Roc.
While this is the first time Luffy's shown using this attack, he's used a similar one in the past, Gum Gum Red Hawk. By coating his arm in Busoshoku Haki, he's able to harden it like steel to touch and even damage Logia devil fruit users, whose bodies taken the properties of various elementals. However, the fast-acting hardening over his contorting rubber body can temporarily ignite his fist on fire.
He first used Gum Gum Red Hawk against Hordy Jones in Fishman Island. In the TV special One Piece: 3D2Y, Luffy discovered this attack for the first time when fighting Brynndi World. In a way, this attack is Luffy carrying on his older brother Ace's legacy by recreating the signature attack that gave Ace the name "Fire Fist."
In One Piece Chapter #1,000, Red Roc takes the impact of the Red Hawk attack one step further. By using Gear Third to inflate his body like a balloon, Luffy can make his limbs reach gigantic proportions and hit much harder. He learned this technique back in Water 7, and it's been a useful piece of his arsenal ever since. Luffy invented this attack by using Gear Third to inflate his fist first and then releasing his Gum-Gum Red Hawk to harden and ignite while scaled to gigantic proportions.
Given its size, naming this new attack after The Roc, the enormous mythical carnivore bird from Middle Eastern mythology, makes sense. This isn't his only attack named after a mythological figure. A number of his Third Gear attacks are named after the Norse God Thor, such as his Gum-Gum Thor Elephant Gun. Several of his Gear Fourth attacks are even named after King Kong, such as his devastating King Kong Gun.
Clearly, this attack is very strong. After all, Luffy uses it to knock Kaido down to his feet. The last time Luffy fought Kaido, in Chapter #923, he used his Gear Fourth to face the Yonko, but none of his attacks seemed to slow Kaido down, let alone hurt him. All it took was a single strike from Kaido's club, with his Thunder Bagua attack, to not only force Luffy out of Gear Fourth but to also leave him completely unconscious.
Since that fight, Luffy's had haki training with Hyogro in the Udon Prison, and the fruits of his labor can be seen with Gum Gum Red Roc. In Chapter #1,000, there's a pained expression of disbelief on Kaido's face as he processes how Luffy was able to damage him. Even Big Mom is in shock by this. This is a good sign of things to come. Luffy's rematch with the Strongest Creature is about to begin.
