The Garp Theory
Now, I cannot take all the credit for this: some one got the ball running on this at Arlong Park and I thought it was very well laid out.
Now, to begin we start at Saobody Archipelago. Luffy and crew are still wandering around and there hasn't been any trouble yet. The very first page of chapter 501 has an underling of Garp's come to tell him news.
The news is that Dark King Rayleigh, the first mate of Gold Roger, has been spotted in the archipelago. Being so closely associated with the Pirate King, he's still a very wanted man. But Garp tells the underling something interesting, "I'll handle this" and then something even more interesting, "Don't go telling any one else, Sengoku included!" Now this is very strange: Garp is a vice admiral and two ranks below Sengoku, the head of the marines, but says that he doesn't want Sengoku to know about this at all. This would be very atypical for the rigid order of the Marines. This will be explained later.
Then, at the end of Chapter 501, we see news spreading throughout Saobody:
Diez Drake reads that the Marines are planning to execute Ace, spurring a war with Whitebeard. This is the first time the public learns of the execution.
However, since it is an order issued by the marines it most likely has been known by the high level Marines for a while. Garp, being a Hero of the Marines and frequently around Sengoku, most likely knew about this before hand.
So, we continue on. Luffy punches Charlos in the face. Uh oh. We see in chapter 504 what Sengoku thinks of the situation:
Sengoku shows no knowledge of Rayleigh being on the island, so Garp's order
has bypassed him. We also see Kizaru tell Sengoku he will go deal with the situation himself. So we continue on down the line and Kizaru arrives at Saobody and beats up every Supernova he finds. Sentomaru, the Axe guy, also shows up and brings the PX models with him. They start having their way with the Strawhats and Kizaru is about to kill Zoro. Rayleigh shows up and saves him in his pajamas. Then, something unexpected happens:
Kuma appears! Why? Why the hell would Kuma appear? Kizaru and Sentomaru have no idea. Well, Kuma does something interesting when he arrives:
Kuma approaches Rayleigh and tells him something. Rayleigh's opinion is disbelief and Kuma says he's not sure if it will happen either.
Then, Kizaru asks Kuma what he is doing and Kuma tells Kizaru he answers to the World Government, not the Marines, and won't tell him anything. Cold. Kuma then continues to paw swipe all of the Straw Hats and send them off the the corners of the world.
But we have to remember Garp! Garp said he would deal with Rayleigh.
But, the only thing that did anything to Rayleigh was Kuma! Not Kizaru, not Sentomaru, and not the Marines. Kuma. Garp and Kuma have connection! This is very interesting! Now, what was Kuma telling Rayleigh? I can only speculate: maybe it was about the execution of Ace and the war with Whitebeard, or maybe some plan we don't know of yet. However, it was not threatening. Let's rememebr this.
Well, what else did Kuma do? He sent the Straw Hats far, far away. But why? Well, he was on an errand for Garp so let's think this through with Garp's mindset. Ace's execution was just announced. Luffy is right next to where the execution will take place. Luffy is Garp's grandson and will surely try to save Ace if he learns about his execution. Garp is very fond of Luffy. Proof:
So I think it's safe to say Garp wanted to save Luffy in what would be a war that is way to strong for him (WB, the admirals, etc). However, this back fires when Luffy learns about the execution on Amazon Lily and vows to save Ace. Impel Down. Blackbeard. Stuff happens and Luffy escapes. Then, we reach the time before the execution: Garp takes his spot next to Sengoku on the execution platform after WhiteBeard arrives.
Garp says he feels no pity for Ace since he's a criminal, but he's family (though not by blood). He is very torn between Justice and his feelings and tears up: one of his grandsons is about to die. Then:
Luffy falls out of the sky into the middle of the war. Garp's plan to have Kuma save Luffy has been for naught and now Luffy is affiliated with White Beard attacking the Marines and is way out of his league.
now, I can't finish the latest part of the theory because it involves the spoilers, but it brings up some
very interesting concepts.