Second Gear is a technique that enhances the user's strength and mobility.
This technique involves Luffy speeding up the blood flow in all or selected body parts, in order to provide them with more oxygen and nutrients. This makes him much faster and more powerful. The technique uses even more oxygen and energy, using up more food and causing Luffy to pant heavily. The increase in his metabolism causes him to be hungrier than usual or even have a paralysis type effect after prolonged use of it, like in the second fight with Rob Lucci, where Luffy was only able to lie on the floor. Lucci, one of the first of Luffy's opponents to witness it, compares the process to doping. Doping is adding more red blood cells to the body part/s, which in turn allows for greater delivery of oxygen and nutrients to the body part/s. In Luffy's case, his organs and blood vessels are made of rubber allowing them to expand and contract at greater rates without tearing. Essentially Luffy increases the blood flow by forcing more blood through his blood vessels thus increase his fighting ability. This mode's enhancements to Luffy's physiology giving him the ability to use a new, stronger set of techniques which are generally the same as his old ones, but are so fast that even a skilled assassin would have a hard time actually seeing them. He developed this ability after encountering CP9, and watching them use Soru.
Prior to the timeskip, Luffy would initiate this technique by using his leg as a pump to increase the blood flow in all of his body parts. As a result, all of his body parts become stronger and faster. The technique used more oxygen and energy, using more food and caused him to pant heavily during use. He has been able to heavily damage some of the strongest individuals in the series while this technique was active, such as Magellan and Blackbeard. When this technique was in effect, his entire metabolic rate went so high that his sweat vaporized rapidly making his body look as if it were steaming and, his entire skin turns slightly pink and shiny from the increased blood flow.
After the timeskip, it appears that Luffy has refined his control over this technique as he has now been shown capable of activating it by pumping blood in only one particular part of his body: the trigger works very fast as he is capable of activating Second Gear in an instant and does not even have to assume his usual stance to initiate it. Thanks to this newfound control over his technique, Luffy now has the ability to select which body parts Second Gear will be active in, instead of having to activate it in his entire body; though the series depicts this as a particular body part undergoing the pumping motion, such as his arm.
Most of the techniques in this mode are named the same as the regular attacks with "Jet" added after the "Gum-Gum" prefix, though often times, Luffy will omit this prefix when using several attacks in succession. The known named techniques that are used by Luffy so far in this form are as follows:
- Second Gear is similar to the Dragon Ball series's technique, Kaio-Ken, as both forms takes the body of the user to the limit increasing their power and speed. In fact, during one of the first times Goku uses the Kaio-Ken, he emits steam from his body, like Luffy does with Second Gear. The resemblance is even more notorious as Luffy's skin turns pink, while Goku's aura is red.