Hangetsu and Seisan were once the same kata, but are now very different

This video demonstrates that kata hangetsu (which Shinkyu no longer do) and kata seisan are in fact the same kata that was adopted by both Shotokan and Goju. Shotokan evolved their kata into hangetsu and Goju into seisan. This is a great example of how different masters and different styles changed and modified kata partly to fit their different styles, to adapt to different interpretations of bunkai, and simply through Chinese whispers.