As Momonosuke reads Oden’s journal, he discovers a passage which in some way reveals the necessity of his survival. Yamato, who also read Oden’s journal made this same declaration earlier in the arc as they were attempting to escape from Onigashima. In that scene, Yamato declared Momonosuke would be the one responsible for bringing the New Dawn and so I think whatever Oden’s journal explains this connection between Momonosuke and the New Dawn.
As soon as Momonosuke begins to explain why his survival is so vital, he is crippled by a voice inside his head. I think this is very clearly the Voice of All Things at work as it’s highly reminiscent of past scenes with Luffy, Roger, Oden, and even Momonosuke himself. The big question here of course is who is speaking to Momonosuke.
There are many possibilities including Momonosuke and the Sea Kings. The scene is similar to Momonosuke’s previous ‘conversation’ with Zunesha, but he here asks ‘who are you?’ when the voice begins speaking, which leads me to believe that this isn’t Zunesha as Momonosuke would already recognize the voice.
If the Sea Kings are going to rescue Luffy, it would also make a lot of sense for Momonosuke to be hearing their voices.
Or what if the voice Momonosuke heard was a species similar to the Mountain God (Giant Boar) and Zunesha (Giant Elephant)?
Denjiro’s line about the Mountain Pigs wreaking havoc in the Flower Capital centuries ago isn’t a throwaway one. It also makes you wonder why Oda would dedicate a whole chapter to this Mountain Pig incident in a flashback which was already going to be packed with so much more things which were relevant to the current and overarching plot. It would only be poetic for the pigs to take the brunt of Onigashima falling, saving the Capital in the process.
This would be consistent with Momonosuke having the ability to control/vicariously see through all these legendary/mythical beasts of the past, especially the ones which played a role during the Void Century.
I would like to put forward the possibility this voice belongs to Joy Boy or Im-sama. The former could make sense if Momonosuke learning of the role he’s meant to play in the World somehow allows him to hear this voice from the past. It could also dovetail well with Kaiddo’s knowledge of Joy Boy, which we learned about earlier in the chapter, if Kaido’s knowledge also comes from the Voice of All Things.
Im-sama is a really interesting possibility in my opinion. Momonosuke does appear to be in distress as this voice speaks inside his head so I could see this being similar to the all seeing eye of Sauron speaking to Frodo when he puts on the one ring. “I SEE YOU”.
*Theory by StrawHatJedi