“Honestly, I’d wanted to add samurai and ninja [to One Piece] at an earlier point in the series.
Debuting two years after One Piece, the Naruto manga ran until 2014 and its TV anime adaptation until 2017, with the One Piece manga not entering the Wano Country arc until the following year, 2018.
To name just a few, the ingredient lists for Demon Slayer, Inuyasha, and Rurouni Kenshin’s recipes for success all include samurai, ninja, katana, and/or yokai.
Creator Eiichiro Oda wanted to incorporate Japanese elements sooner, but held himself back.