Luffy's Most Powerful Form Has Same Weakness as Vegeta's Ultra Instinct
Like Vegeta's Ultra Ego form, Luffy's new "Gear 5" allows him to absorb the energy of a Kaido attack and redirect it in the latest One Piece chapter.
Warning: contains spoilers for One Piece chapter 1046!
One of the few similarities between two manga as thematically different as Dragon Ball Super and One Piece is the way in which some of their characters, such as Vegeta and Monkey D. Luffy, "power up" or otherwise improve their superpowers in battle to become stronger and gain an advantage over an opponent. In One Piece chapter 1045, Luffy's life-and-death confrontation with Kaido, "the strongest creature in the world," forces him to transform into his most powerful form to date: Gear 5. While Luffy's transformation is a spectacular increase in power and abilities, more interestingly for fans is the fact that it mimics Vegeta's Ultra Ego form.
In Dragon Ball Super, "power up" transformations are fundamental to the story's plot. Moreover, for Saiyans such as Vegeta, it's an ability that distinguishes and identifies them as some of the best warriors in the universe. In One Piece, powering-up is not as central to the plot as in Dragon Ball Super, but it still plays an important role, especially in regards to Luffy. At critical moments in the story, Luffy has experienced a power-up transformation or new "gear" that has either allowed him to overcome his opponent or escape what surely would have been a deadly encounter. In his new Gear Fifth form, Luffy has become more powerful than fans ever expected.
Vegeta's Ultra Ego form, which he learned from Beerus, the God of Destruction, is an extremely aggressive fighting style where the ultimate goal is the complete annihilation of one's opponent. To tap into its powers, Vegeta needed the right mindset; namely having the one and only goal of defeating whatever stands in his way. Once that mindset is achieved, Vegeta obtains a sort of super-confidence that makes him impervious to pain. This is necessary because the form's true power is basically to absorb the best and most lethal blows of an opponent and turn them back. Indeed, with each attacker strike, Vegeta experiences a sort of euphoria as his strength is increased by the energy of the hit. The twist to the form is that if Vegeta waits too long to press the attack, either the damage he takes can eventually be taken advantage of by an opponent. or the energy he absorbs will become too much for him to handle. Now, Luffy's Gear Fifth form is giving him the same boost.
Like Ultra Ego, the genius of Gear 5 is that it allows Luffy to absorb every punch, kick, and attack that Kaido can muster and return it back to him. For instance, in One Piece chapter 1046, Kaido hits Luffy with a "Kundali Dragon Swarm" attack that seemingly pulverizes Luffy to smithereens, but instead, Luffy uses his body to redirect the force of the attack into four atom-smashing punches to double Kaido over. However, just as with Ultra Ego's vulnerability, despite the tremendous power Gear 5 gives Luffy, getting walloped by Kaido takes its toll. Indeed, while Luffy has been able to tap into a deep reserve of energy, it seems that even this has its limits. It seems that unless Luffy can defeat Kaido soon, like Vegeta, the damage he sustains will be the end of him. Additionally, the energy he is absorbing from Kaido's strikes seems to be growing beyond his ability to control, as evidenced from the fires staring below the battle.
Any truly god-tier upgrade requires a weakness, and Luffy's new form appears to have the same one as Vegeta's Ultra Instinct. While it's good for One Piece to keep some limit on Luffy so his battles still come with stakes, fans will understandably be worried about the good-natured hero as his fight continues. Luffy may be ambitious within the world of One Piece, but he's far more likeable than Dragon Ball's Vegeta, meaning readers are likely to be way less interested in seeing him take a beating.