One Piece protagonist, Monkey D. Luffy, reached new heights of coolness in episode 565 when he unveiled a recent attack called Gum Gum Red Hawk, or as it is called in the One Piece manga, Gum Gum Fire-Fist Pistol Red Hawk. But while the Red Hawk packs quite a punch, the technical aspect of how this ability works has been a subject of wild theorizing among fans.
Understanding the Red Hawk in One Piece
To understand how the Red Hawk works in One Piece, we must first look at how Luffy's elasticity and rubber-like powers work. It was partly hardcore training, but somewhat also Luffy's ingenuity that helped him develop powerful attacks for combat situations against enemies with devil fruit-fueled abilities that are more equipped for an offense. The Red Hawk specifically also had a more profound, more emotional significance as Luffy had modeled after the late Portgas D. Ace's signature technique, "Hiken" or "Fire Fist", sparking the nickname Fire-Fist Ace.
Gum Gum Devil Fruit
The "Gomu Gomu no Mi" or Gum Gum Fruit is a paramecia-type devil fruit originally belonged to Shanks before Luffy accidentally ate it. The devil fruits in One Piece give those who eat specific powers, depending on the type of fruit the user consumes. This particular devil fruit gives Luffy's body all the properties of rubber - with elasticity, insulation against heat and electricity, and shock-absorption against blunt trauma being the major ones. This offers Luffy the ability to withstand large-scale damage without being fatally injured.
Haki
However, this advantage of Luffy's is nullified by using a certain kind of Haki, called "Busoshoku Haki". Haki is a spiritual energy that exists in everyone in the One Piece universe, although only a few people can use it effectively. Busoshoku Haki, in particular, drastically enhances both offensive and defensive abilities by creating an invisible barrier around the user. It is also one of the only sure-fire ways to counter devil fruit abilities in One Piece, other than maybe drowning since devil-fruit users cannot swim in the ocean.
Gum Gum Red Hawk
One of the primary uses of Busushoku Haki is hardening. Luffy combines his elasticity with partial Busushoku Haki hardening allowing his arm to function almost like a catapult. While he could not ignite his arms on fire like Ace's ability allowed him to do, the Red Hawk was inspired by Ace.
Very possibly, it is the friction of air against the gum-like composition of his fist, combined with the speed of stretching his flexible arm, which results in Luffy's arm igniting into flames to hit his enemies with a hardened, flaming punch.
One Piece fans complained that this power appeared out of nowhere, and Luffy shouldn't, canonically, have elemental powers like Ace. Luffy's Red Hawk requires some amount of science to be rationally explained, the most plausible being that his arm catches fire like how meteorites ignite while hurtling through the atmosphere.
Conclusion
Many theories have suggested that Ace's power was somehow passed on to Luffy, or it was sheer willpower that lets him ignite his arm into flames. But keeping in mind Oda's consistency in adhering to the rules of the One Piece universe, that seems unlikely.
Unfortunately, the explanation of how Red Hawk works is still speculatory in nature, since the One Piece anime or manga does not give us any concrete reasoning for how this ability works. However, no one can deny that the Gum Gum Red Hawk is both effective and a visual treat, and fans hope to see more such badass Luffy moments in the future.