In the latest issues of SBS in Japan, the author of One Piece, Eiichiro Oda answered some questions, including one about Zoro’s family tree!
The family tree goes on for a few generations and confirms that Zoro is a distant relative of Shimotsuki Ryuma.
— Artur – Library of Ohara (@newworldartur) March 1, 2023
Oda explains that Zoro’s family tree includes one known set of grandparents, Shimotsuki Furiko and Roronoa Pinzoro. The two are Zoro’s paternal grandparents.
They gave birth to his father, Arashi. His father married the daughter of a bandit, who gave birth to Zoro.
Oda then talks about Zoro’s grandmother Furiko, the older sister of Shimotsuki Ushimaru, former daimyo of Ringo.
This also reveals that Ushimaru and Furiko were descendants of Ryuma.
So, Furiko descended from Ryuma, and Zoro is related to her through his father.
Hence, Zoro is related to Wano’s most legendary swordsman and even met his ancestor during the Thriller Bark Saga.
As we know, Zoro earned the blade Shusui there, which he eventually swapped for Enma in the Wano Arc.