Character Profile - Coby

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

Tekkai, One Piece Wiki

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

One Piece: Forget Haki, these 5 powers will astonish you with their abilities

If there was a fighter with no devil fruit or haki, but they (somehow) mastered every fighting style. How strong would they be? : r/OnePiece

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

Rokushiki/Tekkai, One Piece Wiki

15 Things You Didn't Know About Haki In 'One Piece

Rokushiki Robin 34 by Shinjojin on DeviantArt

One Piece: Rokushiki Explained - How Strong Was Rob Lucci & CP9? (The Six Powers)