So while there’s a very good chance this mystery character is Hiyori, I think the perhaps more interesting option is Amatsuki Toki.
While it’s hard to tell based on the silhouette alone, it seems the strand of hair actually gets wider at the bottom, which is a closer match to Toki than it is to Hiyori. The strands of hair in front of Hiyori’s face are thinner at the bottom and a bit shorter than Toki’s. Hiyori looks very similar to her mother – almost identical, so this could mean nothing.
Again, it’s really hard to tell from just a silhouette, so I don’t think this is really irrefutable proof, but to me it looks like Toki. She’s the one who delivered the prophecy of Nine Shadows cast by the moon someday liberating Wano, so it would be cool if she made it to the present day to see that prophecy fulfilled.
Given that her fate is left somewhat ambiguous, she could very easily have leapt forward again through time. Not to mention, had Toki died, a time travel devil fruit would be out in the world somewhere and that’s a power which could have some really negative effects if left in the wrong hands. It seems like there could potentially be a number of narrative complications in leaving the time travel fruit unaccounted for and Toki being alive would solve those problems. Not to mention, her origin in the Void Century is likely significant to the central narrative arc of the series, not that I think she’ll reveal to us any details about the Void Century at this point. She clearly understood the meaning of Oden’s words when he spoke of a day 20 years in he future when Wano would be liberated, but she also prevented him from speaking about the events of the Void Century directly.
This ties into an idea I have had for a while that, for some reason, there are things in the One Piece world which cannot be spoken. The Shandoran mandate in protecting the Skypiea Poneglyph says ‘Hold the truth in your heart. Keep your mouth silent. We are the ones who weave history.’ We later see the Five Elders order Clover’s immediate execution just before he can utter the name of the lost civilization and Toki covers Oden’s mouth in 973 perhaps before he can say anything he shouldn’t. I’m not sure if these things are connected, but there does seem to be a pattern. Toki was seemingly born outside Wano during the Void Century and was, for some reason, trying to return to her homeland. Perhaps, if she is alive, her intent will be made clear by the end of this story arc.
Toki’s survival may be significant to the broader narrative arc of One Piece, so if she does turn out to be the character from the end of the chapter, it could lead to some really interesting developments and perhaps give us some greater insight into the Void Century and the importance of opening Wano’s Borders to the world.
Video Review: https://www.youtube.com/watch?v=Xgsg7dRPZbk
*Theory by StrawHatJedi
