Wano’s Prisoner, Big Mom & Kaido
These first two images are panels from Chapter 907: The Empty Trone. From them I’d like to highlight some details in the relationship between Big Mom and Kaido. Kaido owns a “life-long debt” to her, from a long time ago, yet they are still perfectly fine with throwing death threats to each other, therefore it’s plausible to assume that whatever Big Mom helped Kaidou with all those years ago, it isn’t something that gives her power over him. I would guess that this means it was genuine help with something, like a team-up or a deal, yet, she has no control (devil fruit related for instance) over Kaido. Nonetheless, from their reaction faces in the panels it’s also possible to see that Kaidou is clearly affected by Linlin (that even looks a little bit comfortable) and although he is drinking the situation seems very serious. She must have helped him in a big way.
These panels are also from the same chapter and the main things to take way from them are the redundancy of showing that Hina shouldn’t know about Rocks/Locks because of her age and also telling us through exposition that all of this was 40 years ago. Remember, the events resulting in Kaido’s debt were a long time ago, Rocks/Locks was a long time ago. The past isn’t “the past”, if they made a comeback it would be a real threat, even in Garp’s opinion. The last words we saw that Linlin tells Kaido is for them to get along, like the old days.
Also, I can’t be sure about this but Hina’s phrasing is suspicious. How can she say that Garp is a hero because of these events and also not address him directly when she says they lost their Captain?
These panels are from Chapters 921 and 922 and they show Luffy’s reaction to Kaido. They are important because in comparison with other character’s reactions (Shuntenmaru and even Jack), Luffy seems untouched about the situation. In the first one he may be shocked at seeing a dragon but his instinct does not immediately put him in alert.
Finally, these panels belong to Chapter 924 and Oda does two things at the same time. First, the most obvious one: introducing a new powerful character through the fish bone sequence and a silhouette (normally used in One Piece for new characters). The second thing he does is the famous “show don’t tell”. I didn’t see it being talked a lot but Luffy’s glare towards the Prisoner is not only shown through the sound effect but also through the guard that eventually is hit by the fish bone… And the reaction itself: Luffy after being KO’d by Kaidou (to whom he didn’t even react like this), suddenly his completely overwhelmed by this Prisoner. Oda does not draw in vain, he wants us to see this.
Don’t forget, the guards don’t even know if there really his “something” there, this Prisoner’s existence is almost a legend even to the guards that wondered about Luffy before he arrived. Just like Hina shouldn’t know about something from a “long time ago”.
It should be obvious by now, if you read all this, that I’m proposing that this Wano’s Prisoner is the lost captain of Rocks/Locks.
The arguments are quite simple. He is there long enough to have been forgotten, just like the events from a long time ago. Kaido owns Linlin a life-long debt that she has no power over, meaning whatever she helped him with is now under his control (could be anything). Big Mom is more confident while talking to Kaido, than he is with her. If their old captain was alive and free, he would be around, people would know about him. Therefore if he was lost but still is alive then he must me under someone’s control. Luffy’s reaction to him was a big deal, he is a Big Deal! If Kaido and Big Mom do team-up in this “VS. Yonkou Saga” then he would be an extraordinary narrative tool to help them fight the foreshadowed alliance between them.
Also, since Vegapunk was shown in the news this Prisoner isn’t likely to be him (although the silhouette does look alike) and Luffy’s reaction makes me believe that he is unlikely to be a samurai.
*Theory by boredpimpinela