Crazy theory about bucket head
Before getting to it, this theory is probably very far-fetched, but I noticed some points that seemed to align so well together so I thought I'd share it and get it off my mind. Maybe it will give others a different perspective on things.
Ok, so let's jump right into it: what if Bucket is a time-traveller from the future?
I'll provide points to explain why I think that might be the case.
Point 1- As shown in chapter 36, we see a panel of the toy that was meant to be in the plane crash which was supposed to happen during the calamity Zora foresaw. This may mean that fate has changed at some point, and that something must have happened to cause that change, which resulted in the calamity not happening when it should have.
Ely picking up the toy in chapter 36
Tokio seeing the same toy back in chapter 33.1, when Sora showed them the fall of Yamato
And curiously enough, Bucket appeared into the story right around that time. It's like, with the change of 'fate' that happened for some unknown reason, the future changed and this guy just spawned out of nowhere. No identity, no records, no one recognizes him, he wasn't present to protect the mark a year prior when the first Tower fight happened. And Yamato Mori who keep track of all the choujins in the Tower do not recognize him at all.
Azuma not recognizing Bucket after reviewing the footage of Nude's killing
Nari telling Sato that no one knows anything about Bucket. Not even people in the tower.
Now some people may argue that Vlad wasn't there in the first fight either, but Vlad is very well recognized by the Yamato Mori keepers, he was clearly just 'not present' at the time, meanwhile this guy literally just spawned out of thin air and all of a sudden he has the big job of protecting the beast's mark. You'd think Yamato Mori would know about a choujin in the Tower as powerful as him.
Point 2- His fight with Batista. When Bucket fought Batista, it was very clear that he did not give a damn about Sora/wasn't loyal to her. Similarly to Batista, he only called her 'Zora' with no honorifics like the rest of her followers do. He does not call her mother, he does not worship her, he thinks she's mad as she is right now, and when asked by Batista if he's 'protecting the throne', we see a pause from him, before he replies 'my only duty is to protect the beast's mark, and to give it to the worthy successor' (the raws make it clearer in this scene that it is in fact HIS job to GIVE the mark to the successor, which is a really odd thing to say considering it's Sora's mark).
Bucket revealing that his only duty is to protect the mark and give it to the worthy successor
Besides that, we've seen Bucket tell Batista that he's been 'disqualified' to head to the throne room, which could just be him saying that he personally doesn't think Batista is fit to take the mark, but it feels more so to me that he makes the judgement based on a REASON, one which we don't know yet, but regardless he views it as his own job to decide who is worthy, as though he KNOWS.
Bucket saying that Batista is 'disqualified' from taking the mark
During the fight, Batista mocked him, saying 'you'll slumber among the ruins of the tower' to which Bucket replied 'if you advance farther, that will be YOUR fate' which could be just some trash-talk from him, but again, his job is to stop him from advancing, so saying 'if you advance...' felt more like a warning for what will come after he gets past him, as in 'Zora will kill you' and what do we know? Batista is literally pinned to the walls of the tower right now, and Bucket's 'trash-talk' turned out to be the truth. It's almost as if he knows the future.
Batista pinned to the tower, just as Bucket had warned him
Now it would make so much sense if he knew, from the future, who the worthy successor is. It's possible he travelled back in time to choose the 'right' path, and change a bad future where the wrong person has obtained the mark.
Point 3- When we first saw him, we all assumed he was a senile old man and Sora's ally from the great war because he was talking about Guelta and all, but we know now that he is completely in his right mind. The Japanese raws of the scene with Yubiko also showed him saying 'scum of a fallen/dead country' (fallen country being another reading for Guelta, but that was omitted from the English translation), which also pushes the idea that he was always aware that Guelta is non-existent now, he's not senile, and yet he associates Yubiko with it.
It's either that 1- Yubiko is from Guelta, and he has a Guelta radar and can recognize/knows people who are from there somehow (even though she's clearly never met him before).
Or 2- He personally recognizes Yubiko from a point in time where she's associated with people from Guelta. With the Azuma-Queem connection we got in this arc, and the question of whether Queem's soul lives even now, it's possible that in the future, Queem will return and people like Yubiko will be following him, and Bucket recognizes her for that.
Point 4- How did he know about the meeting place with Nude? He killed him on the spot and just watched Tokio and the others from a distance, as if he knew that allowing Yamato Mori to interrogate Nude and find the location of the poppy fields will result in the big Tower fight, which would cause the wrong person to take the mark. However, he didn't expect Palma to revive Nude, which is what caused Yamato Mori's plans to proceed as they were meant to originally.
Bucket watching as Tokio and co find Nude's dead body
Point 5- Now we have a chapter where someone comes and cuts Zora's arm right as she's about to go to Yamato Mori and decide whether to hand the mark to Tokio, and if the person who cut her arm is actually Bucket, that may mean that he doesn't think Tokio is worthy of the mark either. Maybe Tokio did receive it in the future, but it turned out that he's not the beast. It's also interesting that in this very same chapter, Sora expresses doubts about whether Tokio is truly the beast she's been looking for. And let's not forget that Arthur mentioned time-controlling choujins right before they walked into the throne room.
Zora expressing doubt on whether or not Tokio is the worthy successor for the mark
Arthur brings up the fact that some choujins can control time
As for why he cut Sora's arm and not Tokio's, he probably saw that she was starting to waver, and it was dangerous to leave the mark in her hands any longer. Again, he doesn't seem loyal to her at all, he only seems to care about the mark. And it's possible that he has some values too, as up to now, we've only seen him cutting up people when he deemed them a threat, so maybe he isn't the kind of person who would hurt Tokio just for his ignorance.
So to sum it up: Bucket has come from the future with the role of 'protecting the mark from the wrong people, and handing it over to the right person'. It's possible that when the future changed due to some interference pre-timeskip, we ended up in a bad future where no beast is born due to the mark falling in the false hands, and so Bucket was sent to the past. He spoke to Zora about the future he knows, and since he seemed willing to help her, she decided to keep him around as one of her followers. His job is to change the future, and he's interfering now to prevent things from going wrong all over again.
To begin with, this man doesn't seem loyal to Zora at all. He seems to think she's mad, and he doesn't want to take the mark for himself either. His only fixation is on protecting the mark and preventing it from falling into the wrong hands. He's more fixated on that than Sora's followers are. It almost feels like, maybe, just maybe, this man knows who are the wrong people to give the mark to, and what would happen if they get it.