There are several similarities between the two characters and also the characters they interact with.
- They are both extremely skilled swordsmen.
- Their names/titles are slightly similar and hint at being swordsmen. I'm not entirely sure about Roronoa but Kenshin's name was derived from some samurai novel. Also, vaguely note how execution is a main topic in and is constantly mentioned in One Piece and the character Kenshin was based on a samurai who was executed.
- Kenshin was released in 1996 and One Piece came later in 1999.
From ANN's plot summary of Rurouni Kenshin
Himura Kenshin is a vagabond with a dark past and sunny disposition. Not a ronin but a rurouni, he was never a samurai, but an assassin of utmost skill in the Meiji restoration, who in the turning point of the war simply walked away. His travels lead him to Tokyo in the 11th year of the Meiji era, where he befriends a female Kendo master, a former thief, a brawler and a doctor all with their own secrets. Together they fight off the enemies surfacing from the dark past that Kenshin cannot escape. (Seems familiar with a certain character's merry band of men?)
From One Piece plot summary:
... Along his ways, with luck and determination, he finds himself many members who are devoted but to different causes. (Sounds familiar with a certain wanderer?)
So I would like to ask, is there any source that confirms whether the character Roronoa Zoro from One Piece is related in any way to Kenshin, or whether One Piece is somewhat influenced by Kenshin?