No two One Piece fans are likely to 100% agree on how they think the series will end, and one such debate surrounds which opponents Luffy has left to fight. Nearly every fan agrees he'll come to blows with his archrival Blackbeard. Luffy’s idol Shanks is another viable contender -- while there’s no animosity between the two, their vow to meet again kickstarted the entire series, and as one of the Yonko, Shanks is an obstacle in Luffy’s path to claim the throne of Pirate King.
Then there’s the Fleet Admiral of the Marines, Sakazuki, also known by his alias Akainu. While Luffy and Sakazuki have history together -- and a grudge with one another -- the fact that Sakazuki isn’t a pirate -- nor is he gunning for the Pirate King’s throne -- means many One Piece fans don’t believe they will fight. At the very least, it’s unnecessary in terms of Luffy achieving his dream. Despite this, it’s almost guaranteed that the two will clash eventually -- here's why.
Sakazuki is the man who killed Portgas D. Ace, Luffy’s brother, before the Straw Hat captain’s very eyes. To this day, Ace remains unavenged, and given how deeply his death impacted Luffy, it’s unlikely One Piece will end without the Straw Hat captain amending that. A few chapters later, Oda decided to give the two a permanent physical connection as well when Akainu burned Luffy across the chest, giving the protagonist his now-famous scar. This scar has since become an iconic part of Luffy's character design, and also serves as a constant reminder of the unsettled score he has with the villain who inflicted it.
Two years later, Jimbei informs Luffy of the big changes on the world stage he'd missed during his training on Rusukaina Island: Blackbeard’s ascension to Yonko status, and Sakazuki’s rise to the Fleet Admiral position. It’s at the mention of Akainu specifically that Luffy’s scar throbs, reminding readers the mark across his chest is more than just for show. Even two years after the Marineford arc, Luffy’s trauma lingers. This scene reaffirms Sakazuki’s position as a threat on par with Blackbeard, and one of the two figureheads of the current world order that need to be taken down.
While we don’t know how One Piece's ongoing Wano arc will end, Luffy seems set to defeat the Yonko Kaido. Some fans argue this means Luffy will be above Akainu in the series’ pecking order -- as mighty as the Admirals are, they have been shown to be below the Yonko strength-wise. However, as Fleet Admiral, Sakazuki is in a higher tier compared to where he was as a regular Admiral. Even back then, Sakazuki already possessed the strongest offensive Devil Fruit, trading blows with and eventually inflicting mortal damage on Whitebeard himself, the world’s strongest pirate. Sakazuki and his Magma-Magma Fruit are overwhelmingly powerful, and if he’s grown in the two years since, there’s no doubt he currently stands as one of the strongest characters in One Piece.
One reason some fans dismiss the possibility of a Luffy/Sakazuki fight is that there's another contender to take out the Fleet Admiral. Sabo is the Revolutionary Army’s chief of staff, Luffy and Ace’s blood brother, and the inheritor of Ace’s Flame-Flame Fruit. As such, many have pointed out how apt it would be for Sabo to succeed where Ace could not. While it’s plausible he will help in the fight against Akainu, it’s unlikely to be a solo effort. Sabo simply doesn't have the personal connection to Sakazuki that Luffy has, and moreover, Sabo has stated he bears no grudges for Ace’s death, as it was Ace who chose the pirate’s life and all the consequences it entails.
This isn’t the case with Luffy, who scowls at the thought of Akainu even two years later. As far as he's concerned, Sakazuki is responsible for Ace’s death and represents more than just the Marines' current leadership -- his ideology of Absolute Justice has led to the series' greatest atrocities. One Piece kicked off with Luffy and Zoro teaming up against tyrannical Marine Captain Morgan, and since then, the Marines have served as antagonists in many of the series’ arcs, also having a direct hand in the traumatic backstories of several of Luffy’s crew.
If Luffy is the man to usher in a new era, as has been purported, then the old world order must fall by his hand -- including the corruption of the current Marine regime. Sakazuki represents both that corruption and the physical manifestation of a threat that has existed since the beginning. It would be a disservice if anyone other than the One Piece protagonist were to bring an end to that threat.
Fans are understandably worried that there may not be time to resolve every narrative thread, or for Oda to depict everything he wants by the time One Piece ends. However, there’s simply far too much evidence to support Luffy taking on the fearsome Fleet Admiral by the end, and it will no doubt make for one of the most enthralling battles ever committed to the pages of Shonen Jump.
