I think the rhythm of someone’s heart is also their “voice” in the One Piece world, in a literal sense. They repeat over and over through lives (hence, inherited will), but rhythms are, well, drum or heartbeats.
Luffy’s voice vanishes, but Zunesha recognizes the heartbeat of Luffy as Joyboy.
Moments later, Luffy is alive. His heartbeat changed. Luffy never died, it’s just no one recognized Luffy’s new heartbeat, and thus his voice is gone.
When Zoro almost dies. He hears a drum beat alongside the voice of objects. He literally hears their “rhythm”. All things have a heartbeat or a rhythm of some kind.
When Law switches the hearts of characters, their personalities change completely. This is because the heartbeat, and the voice, of the character is different. However, the character’s devil fruit power doesn’t change. I know this is a silly point, but hear me out.
The “rumble” ball changes the rhythm of the body.
When you eat a devil fruit, it changes the rhythm of someone’s body to that devil fruit’s power. Like when Zoro heard the voice of a rock, then someone with the rock rock fruit’s body exhibits that same heartbeat or voice that Zoro heard.
But people’s hearts have a different rhythm. Awakening is when those two things have the same rhythm. This is why someone would achieve “enlightenment” if the Hito-Hito no Mi is eaten by a human being, they already have the same rhythm to begin with! You wouldn’t need to awaken through hard work to make them exactly the same.
The reason Zunesha recognized Joyboy is Luffy finally transformed his heartbeat to be in alignment as his body’s voice. His body is that of Nika, and the same body that Joyboy also inhabited and awakened at one point. Zunesha can only hear the heart of a person, not the rhythm of their body, so it’s only when Luffy awakens does Zunesha hear him. Otherwise, Zunesha would be able to hear the voice of everything.
Oda said it best almost 1000 chapters ago:
The heart of a character is literally their “voice” in One Piece. Therefore, the “voice of all things” is the ability to hear the heartbeat of everything, living or inanimate. Zoro got a very small preview of that in Alabasta.
In addition, this gives Blackbeard the most dangerous powerset in the One Piece world. Why?
The darkness fruit “stops” the rhythm of something. This is how it stops powers. The earthquake fruit can “change” the rhythm of something through vibrations. This effectively gives Blackbeard the ability to change the way matter operates similar to Luffy’s awakening. Because of this, his fight with Luffy’s will be supremely cartoony.
So what about Lineage Factor?
Pretty simple. Your DNA is intertwined with your rhythm. That’s basically it. It was easy to make smiles because it’s way easier to use a living thing, which has a rhythm or at least the DNA to express that rhythm, as the source material. If you take a living giraffe, and put the heartbeat of that into the body of a person, bam, you have a devil fruit. If you change someone’s DNA when they’re a child, then they’ll have a totally different rhythm or voice, or vice versa.
All things have a voice, including things like trees and rocks.
That voice is literally a rhythm, or a drum/heartbeat. If a rock has a heartbeat, then when you eat the rock fruit, your body now has that rhythm and becomes like a rock. So Luffy’s fruit works because his body changed to the rhythm or heartbeat of Nika. Awakening is when the heart of the person and the rhythm of their body reach alignment, and thus why Zuneisha didn’t recognize Joyboy/Nika’s fruit until Luffy awakened.
This also explains why devil fruits use a sort of onomatopoeia for their naming convention.
Wills work the same way. When someone inherits another persons will, then their heartbeat is the same. This is why people think Luffy has the same energy as Roger, they quite literally have the same voice/heartbeat. Devil fruits, which affecting the rhythm of bodies, also reincarnate.
This could also explain why most people can’t eat more than 1 devil fruit, as that many heartbeats/rhythms would throw their heart out of sync and cause them to die. Blackbeard may have multiple hearts/rhythms allowing him to have more devil fruits or maybe certain fruits rhythms can sync up, but nobody every got it correct before blackbeard.
Therefore, I think Devil Fruits are the “wills” or the heartbeat of someone or something that used to be alive in the past, or they modify the body’s DNA to change its rhythm.
Rhythm is all. It’s the fundamental underpinning of how One Piece works.
Theory by IDIOTLORD (https://www.reddit.com/user/the_idiotlord)