The Six Powers, Wiki

Rokushiki - One Piece

The One Piece Is Real: Fighting Styles

Jabra's Powers ONE PIECE GOLD

Rokushiki, Wiki

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

Chapter Discussion - Rokushiki is based on Haki, Page 7

Rokushiki/Shigan, One Piece Wiki

Rokushiki/Shigan, One Piece Wiki

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