Nico Robin haki kick color by xMrNothingx on DeviantArt

Rokushiki, One Piece Role-Play Wiki

Rokushiki + Haki Robin action scene storyboard by Shinjojin on DeviantArt

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

Rankyaku, One Piece Role-Play Wiki

What if Rokushiki is Haki based?

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

Was Rob Lucci's Rokuogan an application of the advanced Haki that Luffy is learning now? - Quora

Powers & Abilities - New Level CoO + CoA Combination Technique..

One Piece: 10 Characters You Never Knew Possessed Haki

Chapter Discussion - Rokushiki is based on Haki, Page 5