Summary
Nika was first introduced inOne Piecetowards the end of the Wano and has been growing in terms of relevance and popularity ever since. Essentially,the Sun God Nikais the same person also known by the name of Joyboy. Whoever ends up using the powers of Hito Hito no Mi, Model: Nika ends up becoming the Sun God itself.
However, not just anyone can eat this Devil Fruit. This Devil Fruit is of the Mythical Zoan class, which means that not just anyone can consume it since it has a will of its own. Luffy ended up eating this Devil Fruit because he was the perfect candidate for being Nika. However, hypothetically speaking, if Luffy did not eat this Devil Fruit, there are other characters in the series who were potential candidates as well.

5Monkey D. Dragon
Devil Fruit: N/A
Dragon is an incredibly powerful characterand, at the same time, one who fights for the freedom of people. He is the head of the Revolutionary Army and his goal is to rip the Celestial Dragons from power, root and stem. He wants to create a just world order where the powerless are not being prayed upon by the powerful. Dragon could easily have been Nika had Luffy not eaten the Devil Fruit.
Of course, there are major differences when it comes to the personalities of Luffy and Dragon. Luffy is willing to help everyone around him at the cost of his own life. Meanwhile, Dragon chooses to be more calculated, as seen when he chose not to do anything about Ginny’s capture.

4Sabo
Devil Fruit: Mera Mera no Mi
Just like Dragon,Sabo is another person who could easily have been Nika.Fans know that Sabo was born into nobility, however, he immediately realized how corrupt life in the Goa kingdom was. That is why Sabo ended up leaving his position as a noble and decided to set out to see. One thing led to another and Sabo ended up joining the Revolutionary Army.
Now, he’s fighting for the freedom of the world and, unlike Dragon, he doesn’t take a pragmatic approach. Sabo will save anyone and everyone around him, no matter the cost. He is an incredible character who believes in the true value of freedom and wants to crush those who oppress the weak and the poor. Sabo could easily have been Nika had Luffy not eaten the Devil Fruit himself and he certainly would have been a great candidate for this role as well.

3Portgas D. Ace
Ace is Luffy’s elder brother and a character who had a profound effect on his life. Ace had chased freedom throughout his life and wanted to live a life free of regrets as well. Fans knew Ace to be a very kind-hearted and gentle character who cared for all those around him. He would go to any lengths to save those close to him, especially his friends, which is a quality that he shares with his brother, Luffy.
Ace was the leader of the next generation and, in the eyes of many, he should have been the next Nika. Even Roger, his father, believed that his son would be the one to find the One Piece and, thus, end the World Government and their tyranny. There are many characters who likely believed Ace to be the leader in the next Great War, however, he ended up dying while protecting his brother.

2Gol D. Roger
Roger himself would have been a fascinating candidatefor the title of Nika had he managed to eat the Devil Fruit. When it comes to personality, Roger was just like Luffy. This is highlighted time and again in the series, however, the biggest proof that fans have of this is the fact that both Roger and Luffy have the same dream.
Fans do not know what this dream is just yet, however, it will be revealed to them later down the line. Both of these characters are alike in many ways and Roger could easily have been the perfect Nika had the opportunity presented itself. Unfortunately, he was too early, as he confessed himself and, thus, Luffy ended up becoming Nika.

1Bartholomew Kuma
Devil Fruit: Nikyu Nikyu no Mi
Undoubtedly, the most deserving character for the position of Nika other than Luffy himself is Bartholomew Kuma. Fans knowKuma to be an incredibly important characterinOne Piece.Recently, in his flashback, fans found out that Kuma was born into slavery and led a very tragic life from the get-go.
However, his conviction in Nika never faded. He even wanted to be more like Nika and, because of that, he has helped countless people throughout his life at his own expense. Kuma is an amazing character with the kindest of hearts. He has saved countless lives, including those of slaves over the years. If that wasn’t enough, Kuma is still fighting even when his own consciousness has been lost to the Pacifista Project. He’s an incredible character and certainly would have made an incredible Nika as well. Kuma still hopes that Nika will come one day and save the world from its misery.

One Piece
Cast
One Piece is a Japanese manga written and illustrated by Eiichiro Oda. The series follows protagonist Monkey D. Luffy and his Straw Hat Pirate crew as they explore the Grand Line to find the King of the Pirates' ultimate treasure, the One Piece, in order to become the next king. The manga’s popularity helped it spin off into a larger media franchise, including an anime with more than 1,000 episodes.