Shigan, Wiki

The Nico Robin: Rokushiki Style Project

World of Shinjoin! — The Nico Robin: Rokushiki style Project! (part2)

Chapter Discussion - Rokushiki is based on Haki, Page 7

Chapter Discussion - Rokushiki is based on Haki, Page 5

Rokushiki/Shigan, One Piece Wiki

Rokushiki Robin 25 by Shinjojin on DeviantArt

Kenali 7 Teknik Rokushiki di One Piece!

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

One Piece OP Spells (Lucci) - Shigan Fruit Form

Shigan, Wiki