WARNING: The following contains spoilers for One Piece Chapter #1023, "Spitting Image," by Eiichiro Oda, Stephen Paul and Vanessa Satone, available in English via Manga Plus and Viz Media.
In the world of One Piece, there are many conflicting philosophies and ideologies. This conflict extends to the fandom, where many people debate what plot points could mean and what might be in store for the Straw Hat pirates in the future. Case in point, recent events in the manga have got fans refocusing on the concept of Inherited Will, with some resurrecting old theories that say Inherited Will might be physical reincarnation rather than a simple philosophical concept.
In the most recent chapter, Chapter #1023, Zoro fights one of the Tobbi Roppo, King. While this battle happens, Kawamatsu and Hyogoro, two allies to the Straw Hats, watch from afar and discuss Zoro's skills. Kawamatsu says they didn't mind it when Kozuki Hiyori gave Zoro one of the 21 Great Grade swords. Hyogoro agrees with this, noting that Zoro looks a lot like a young Shimotsuki Ushimaru, the last daimyo of Ringo in Wano Country. Famously, Shimotsuki Ushimaru inherited his swordsmanship skills from his ancestor Shimotsuki Ryuma, and both Shimotsuki Ryuma and Zoro are one-eyed swordsmen.
Kawamatsu also notes that Zoro returned Shusui, one of Ryuma’s swords, to Wano, something he considers to be an act of fate. The tone of Kawamatsu and Hyogoro's conversation suggests that they don't see these events as a simple coincidence; rather, thinking that there is something more at work.
This isn't the first time the power of lineage has been mentioned in One Piece. The concept of Inherited Will was first brought up in a quote from former Pirate King, Gol D. Roger. Inherited Will is the idea that people will pass their dreams and ideals to future generations, allowing their desires to be fulfilled even after they've passed on. The original quote is focused on the passing of ideas and values, but the more you consider the concept and the One Piece universe at large, the more it makes sense that this could be actual reincarnation.
Inherited Will isn't the only will found in the series. A core mystery in One Piece is the Will Of D, a concept that links everyone who has a 'D' middle initial, including the series' protagonist, Monkey D. Luffy. In fact, Luffy's family all have the D initial in their name, from his father, Monkey D. Dragon to his grandfather, Monkey D. Garp. But it isn't just Luffy's family. We've been introduced to others with this initial, like Luffy's adopted brother Portgaz D. Ace and ally Trafalgar D. Water Law.
Currently, it is unknown what the D in One Piece means. As a result, the fandom is full of theories about the mysterious letter and its significance. There is at least one major canonical clue, however, revealed during the battle at Marineford. During this battle, Whitebeard, someone who knows the meaning of the D, says that killing someone with a D in their name would not end the current conflict as someone else would simply inherit and carry on that person's will, suggesting a link between the Will of D and Inherited Will.
In addition, Donquixote Rosinante noted that in his home country, people with the D initials are said to be from the Family Of D, a group also known as the Natural Enemy of God. This family is also the enemy of the Celestial Dragons, the aristocratic descendants of the people who established the World Government. This suggests that these two forces might be locked in an infinitely repeating struggle that continues generation after generation.
All of this also ties into Joy Boy, the enigmatic figure who left the legendary One Piece on the last island of the Grand Line. According to legend, Joy Boy will return when the appointed time comes. However, no one really knows what that time is. Many in the One Piece fandom have speculated that Luffy is the reincarnation of Joy Boy, though Kaido, the Governor-General of the Beasts Pirates, claimed that Luffy couldn't be Joy Boy after he defeated him during the Onigashima Raid.
The mere mention of this means that Kaido must believe in reincarnation -- why else would he even consider the idea? This, mixed with the comments made by Whitebeard, Kawamatsu and Hyogoro, seems to suggest that the belief in reincarnation is common in the One Piece universe, even if the Straw Hats are not aware of it.
The more you think about it, the more the reincarnation theory makes sense. While it is common for folklore and grudges to pass from generation to generation, the cycling history of One Piece seems to go beyond that. The characters seem to be performing actions and resolving old grudges that they are not fully informed about, suggesting that some otherwordly force is indeed guiding their hand. This becomes even more true when you realize that those with the Will Of D are not directly related, implying that something larger is at work. However, we will not know if this is fate, reincarnation or something in between until creator Eiichiro Oda decides to reveal it to us.
