One Piece's Wano arc has ended the first phase, and all the pieces are in place for the big fight with Kaido as the arc continues. But these pieces also include the introduction of new entities as well.
In the latest chapter of the series, a character, shrouded in shadow, gets a big introduction as fans learn a little about how Kaido's prison works.
When Luffy is thrown into prison at the end of Chapter 924, there's a brief reveal of some of the other prisoners there. While one is not shown directly, fans learn that he's being fed poisonous fish. It's usually meant to execute prisoners, but he's the only one that lives off of them (and being fed one fish a day)
Another important thing of note is that when he's been fed the fish, the guards are told to de-bone them. But one guard laughs off this ridiculous seeming rule, and pays for it soon enough. As Luffy is being escorted to his cell, the guards are distracted a bit and one of them is stabbed in the neck by fish bones.
The mysterious stranger had spit them out of his mouth and into the guard's neck. The guard survives, but the other guards mention that no one knows what resides in that cell. The only thing fans see after this is a pair of striking eyes hiding in the shadow. As for the identity of who this can be, it could be any number of characters in the One Piece world.
Luffy shares a cell with Eustass Kidd, another one of the Supernovas, and Hawkins and Law have appeared as well. So it could be either another one of these, or it could be one of the legendary samurai that Kinemon had mentioned a few chapters prior. Kinemon said that Luffy and the others should find three of his fellow samurai who fought with him 20 years ago, and one could be right in the prison with Luffy.
Fans will know for sure soon enough, though the mystery is going to be tough to crack without more clues. Eiichiro Oda's One Piece first began serialization in Shueisha's Weekly Shonen Jump in 1997. It has since been collected into over 80 volumes, and has been a critical and commercial success worldwide with many of the volumes breaking printing records in Japan. The manga has even set a Guinness World Record for the most copies published for the same comic book by a single author, and is the best-selling manga series worldwide with over 430 million copies sold.
Oda revealed that he was about 80-percent done with the manga at this point with the Wano arc, fans are worried that the series may be coming to an end sooner than they thought. But it wouldn't be wrong to infer that the ending will most likely still be years away given how much of the world there is to explore and just how well it's selling week to week.