As we can see here in this video, Marco rushed up to stand up against Kizaru’s attack. Now then, to prove that Marco has Observation Haki, we have to break apart this video and relate it to some manga scans.
[video=youtube;BvDaX9r5Bc8]https://www.youtube.com/watch?v=BvDaX9r5Bc8[/video]
Now, the first thing that should be pointed to in the video is that Marco blocked Kizaru’s Magatama attack in a partially transformed state, not as a full Phoenix. This is important, because it ties into the main point: Marco cannot heal attacks he received on his normal human body with the blue flames.
The flames can only heal Marco if they were present on the part of his body that received a wound prior to receiving the wound. The proof can be found with this:
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Marco receives a sneak attack from Kizaru from behind while in his human body, leaving two wounds on his back and chest.
Now, here in another chapter, while Marco is summoning up his flames, we can clearly see the wounds are still present as blood can be seen trailing from them.
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Now, what’s important is that we look at what’s happened in between this page and the page where Marco is wounded in the first place.
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We have Jozu being frozen by Aokiji
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We have Sakazuki piercing Whitebeard in the chest
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Then we have Luffy arguing with Iva and receiving the tension hormones
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As we can see here, Sakazuki has backed away from Whitebeard and WB has slumped to his knees, showing that Luffy and Iva start arguing AFTER WB is struck, not before or at the same time.
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Then you have Luffy running towards the execution stand with Iva and knocking down some Marine fodder.
Then you have Luffy having a brief confrontation with Coby, then you have Pacifista blocking his path, then Hancock saves him and finally, we come full circle to Marco summoning up his flames with his wounds intact. Now, Marco isn’t stupid, and he’s an experienced fighter in the New World and he’s dead serious about this war. So, with that in mind, why would he not heal his wounds? We’ve had all that happen in between the two panels, Marco has had ample time to transform and start healing, but he hasn’t, and it makes no sense to say that Marco would just leave two wounds like that intact if he can get rid of them. The only sensible answer: He can’t. He can’t heal wounds that were dealt to his direct body, which would also explain the bruises he got after Garp punched him with Haki, and them not healing despite being fully transformed at the time.