Gomu Gomu no Mi/Gear 5 Techniques

I can do everything I wanted to do!! I think I can fight a bit longer... My heartbeat sounds so funny!! This is the pinnacle of what I can do!! This is.. Gear Fifth!!!

Gear Fifth is a technique created as a result of Luffy awakening his Devil Fruit. It was first seen after Luffy was defeated by Kaidou on the Onigashima rooftop.

Overview
The awakening of the Gomu Gomu no Mi, also known as the Hito Hito no Mi, Model: Nika, grants the user's rubber body increased strength and freedom. One of the most notable features of the awakened form is granting cartoon-like effects, not only to the user, but also to their opponent, an example being eye-popping effects.

It allows him to do Gear Third like body inflation without physically pumping air, which he first used against Kaidou. He was able to increase his arm to an enormous size in order to grab Kaidou's transformed body and drag him up out of the Skull Dome. With his enlarged limbs Luffy could manhandle Kaidou despite his enormous size, swinging him from side to side.

Luffy's rubbery nature can be extended into the environment around him, as seen when Luffy stretched a section of roof and used it to repel Kaidou's Boro Breath back at him. Interestingly, the altered terrain, while elastic, was neither burnt nor melted by the Boro Breath, even though the attack was shown to be scorching hot and had enough explosive power to destroy a castle.

In this state, Luffy's heartbeat takes on a musical rhythm which has been described by Zunesha as the "Drums of Liberation" (解放のドラム).

Trivia

 * Gear Fifth seems to take inspiration from rubber hose animation and various cartoon effects.
 * Gear Fifth was first hinted at in SBS Volume 98, when a fan asked if it was coming and Oda responded by surreptitiously noting that the world was in the process of transitioning to 5G broadband networks.