Nico Robin haki + rokushiki by xMrNothingx on DeviantArt

Rokushiki

One Piece Gold - Rob Lucci's vivre card said that: The training required for the acquisition of rokushiki is akin to that used for acquiring haki. Akin = in the family Rokushiki

Vivre Card Databook – Index Set (some new information) – The Library of Ohara

One Piece: Strongest Powers That Aren't Haki

Shigan, One Piece Wiki

Artur - Library of Ohara on X: Official Vivre Card Correction: Lucci's vivre card said that he learned haki during the timeskip. However, this correction states he simply strengthened his haki over

Konoha: Deduce Rokushiki and Armament Haki at the Start! Latest Chapter - MTLNATION

Chapter Discussion - Rokushiki is based on Haki, Page 5

☠ Sistema de Treino ☠ - One Piece

Rokushiki is based on physical strength is actually based on a mistranslation in earlier One Piece volumes : r/OnePiece