Oda is known to be a brilliant writer and his story has left an impression on fans all over the world. The storytelling in One Piece is the primary reason why many fans hold it so close to their hearts and often to an entirely different standard when compared to any other manga series. Oda's One Piece is a product of love and incredible creativity, coupled with terrific vision and fantastic story writing.
One Piece is a story where fans know their characters very well and Oda makes sure that all of them never stray from what they truly believe in. As such, it is quite easy to guess what direction character arcs often take. However, at times, Oda has gone beyond and absolutely stunned his fans by subverting their expectations.
5 The Event Of Sabaody Archipelago
Up until Sabaody Archipelago, the Straw Hat Pirates triumphed at every island they went to. They started from the East Blue, where Luffy became the meanest man and acquired a massive bounty of 30 million berries, known to be staggering for that sea, to the Grand Line, where he defeated a Warlord and attained a 100 million berries bounty. In Enies Lobby, Luffy and his crew managed to do the impossible and saved Robin from the clutches of the Government and Thriller Bark was no different.
Yet, Sabaody Archipelago is where fans received their first shocker. Against all expectations, the Straw Hat crew was utterly decimated by the Navy and Bartholomew Kuma. Its impact was such that even to this day, fans hold Sabaody Archipelago in a different light. Not because the arc is better than every other in the story, but simply because it gave the Straw Hat crew their first reality check before they eventually went on to conquer the New World as well.
4 Ace's Lineage
Oda is brilliant at writing character arcs and One Piece has no shortage of some of the most brilliant characters in all of fiction. Luffy's older brother, Portgas D. Ace, is one such character. Ace was introduced to the fans in the Alabasta arc of the story and ever since then, fans knew that he would play an important role moving forward, given that he was Luffy's brother. When Ace was captured and handed over to the Navy, it was expected of Luffy to rescue Ace.
However, fans expected Dragon to make a move as well. In fact, even Ivankov, one of the commanders of the Revolutionary Army, expected Dragon to make a move as most fans just assumed that Luffy shared a blood relationship with Ace. It wasn't revealed until his execution began that Ace was actually the son of none other than the Pirate King, Gol D. Roger and that Luffy and Ace were just sworn brothers instead of blood brothers. To be fair to the fans, this is something that Oda decided spontaneously rather than having it planned out but it worked well all the same.
3 Ace's Death
Portgas D. Ace was an exceptionally important character, more so than ever during the latter part of the first half of One Piece. After his capture, Ace was the trigger for the biggest war in the Great Pirate Era up until that point. Expectedly, the likes of Luffy and the Whitebeard Pirates, who Ace had a very close connection to, ran to his aid and eventually fought in what is known to be the Paramount War. Oda drew two entire arcs focused on the rescue of Ace.
As such, one would expect him to be rescued at the end of the day. In fact, Luffy even managed to rescue Ace from his shackles in the Marineford arc, however, Oda had other plans. Shortly after being saved, Ace ended up sacrificing himself to save Luffy's life from Akainu. Within a flash, his life was taken from him and the fans were left in a state of utter shock. To this day, this remains to be the most shocking thing about One Piece and no fan saw it coming. In fact, Oda's very own editors tried to advise him against killing Ace off.
2 The Minks' Loyalty
In the Zou arc of One Piece, fans saw a character named Raizo being made central to the plot. Luffy's group, which, at this point, carried Kin'emon and Kanjuro with them, were looking for another samurai from the land of Wano called Raizo. Somehow, one of Kaido's underlings, Jack the Drought, also had information that Raizo was being kept at Zou. So, he invaded the land and tortured all the citizens for 10 days. At the end of all this, he poisoned everyone there and left them to die. The people of Zou kept repeating that Raizo was not on the island and that they had no information on any such person.
In fact, when Luffy and his crew arrived on the island, the word "Samurai" was thought to be forbidden there because of how much pain it caused every single citizen of the island, including the children. However, shortly afterwards, it was revealed that the samurai named Raizo was indeed on the island and was being protected by the people of Zou at the cost of their lives. When asked why, Nekomamushi simply responded that they would never sell out a comrade to anyone. Undoubtedly, this remains one of the biggest shocks in One Piece as Oda fully convinced his fans of the fact that Raizo would not be on the island and that the people of Zou would have no connection to him whatsoever.
1 The Nika Fruit
Devil Fruits play a massive role in the One Piece world and, with time, their importance has only grown in the series. Luffy, the protagonist of the story, is a user of these powers and was, in fact, the very first person to have a Devil Fruit in the manga when he ate his Gomu Gomu no Mi in the very first chapter. As such, fans were incredibly familiar with his Devil Fruit and its powers, given that he is the devil fruit user everyone sees the most. In the Wano Country arc, however, Oda flipped the script entirely. In Luffy's fight against Kaido, it was revealed that his Devil Fruit is actually not the Gomu Gomu no Mi at all.
After Luffy was struck down by Kaido, his Devil Fruit started to awaken, and soon after, it was revealed that his fruit is actually a Mythical Zoan type named after a God. The true name of Luffy's fruit was revealed to be the Hito Hito no Mi, Model: Nika and it was also explained that having the power of rubber was actually not the real power of the fruit but just one of the attributes of this ability. In fact, the real power of the Nika fruit was to spread laughter, joy, and freedom wherever he goes and, at the same time, fight with the most freedom himself.