Rokushiki - One Piece

Rokushiki, Wiki

One Piece: Rokushiki, Explained

Character Profile - Rob Lucci

Illustration - Rokushiki Robin artwork

Nico Robin Hana Rokushiki Combo by Fighter1Manga on DeviantArt

Rokushiki Robin 32-2 by Shinjojin on DeviantArt

Chapter Discussion - Rokushiki is based on Haki, Page 7

Rokushiki Robin 25 by Shinjojin on DeviantArt

Honestly Oda probably should have just expanded on Rokushiki instead of creating Haki. He could have definitely made it to where there are techniques that allow you to hit logias and armament

Shigan, Wiki