Popular opinion holds that the five Pinan / Heian kata were developed by Itosu sensei on Okinawa to include key movements from Kusanku (perhaps along with the two 'lost' Channan forms) interspersed with more basic techniques to make teaching easier to larger and younger classes. Master Kousaku Yokota (Shotokan Karate Myths) suggests that Heian Nidan is a simplified version of this kata in its entirety. Consider also that Shotokan's Heian Nidan is still taught as Pinan Shodan on Okinawa, or the first form learned perhaps betraying the importance of Kushanku on its development and the key role this latter pattern plays in the Itosu system.
Author Nathan Johnson offers a very different idea in his book The Great Karate Myth when he argues that originally this kata was meant to be performed with a pair of sai. In particular, the 'knife hand block' is interpreted by Johnson to be a block with a sai. In the Okinawan version this move is performed in cat stance which, Johnson again argues, allows a swift front kick to kick away the weapon trapped in the prong of the sai or to kick the weapon wielding hand. As with his theories on the Tekki kata however, he offers no direct evidence for his hypothesis.
Johnson also notes that we do not in fact know if 'To te' Sakugawa learned Kusanku 'as is' or if his version is a synthesis of something (or various things) he was taught.
The name of the kata means 'To look to the sky', a reference to the simple but compelling opening movements of the form as the arms are slowly raised with a small triangle formed between the hands.
Master Kanazawa performing Kanku Dai
