This Guest Post is by my friend and senior, Sensei Pat Nakata. Nakata Sensei is the head of the Okinawa Shorin-Ryu Karate Association in Hawaii. He was a student of Chosin (Choshin) Chibana in Shorin-Ryu, and also studied Ryukyu Kobudo under Sensei Fumio Nagaishi. When he was a young man, he studied Wado-Ryu Karate under Sensei Walter Nishioka.
In the Chibana Shorin-Ryu Karate Kata curriculum, osae is taught and stressed in the Kihon Kata and the Naihanchi Kata, after which, the whole concept of osae is forgotten for the other Kata. As in Goju-Ryu, most Karate Kata have osae, but most Karateka do not know the concept of osae. For example; if one was to block and kept that block without releasing (hazusu / hazusanai) that end position and did a kick holding that block position, that block was then an osae. That being said, many Karateka do osae when practicing "fighting" techniques. Most of these Karateka question the effectiveness of Kata for real combat. Well, how can a Kata be effective, when there is no osae? In other words, there is no practicality for true combat situations, such as closing or entering the opponent(s).
Most Kata performances I witness are when the Kata performer enters one pose after the other. There is no concentration on the transition (be it osae, clearing, etc.) from one technique to the next. As soon as one technique is completed, there is an immediate transition to entering the next technique. This transition covers the "space" between the techniques. The transition is the fighting application of the techniques. So, the effectiveness of the fighting technique (within the Kata) is dependent upon the execution of the transition, other than just the technique. For an example, one can have a strong punch with good body mechanics, but will not be able to apply it without entering the opponent (osae).
This entering or osae is the transition "technique" that makes a Kata an effective fighting practice. What good is there in having strong techniques when one does not know how to effectively enter the opponent? In the teachings of Chibana Chosin Sensei, "there is osae in every move of the Kata".
I was fortunate to have been able to listen to a discussion between Ueshiba Morihei Sensei (founder of Aikido) and Otsuka Hironori Shihan (founder of Wado-Ryu Karate) on "real" fighting application. Both masters agreed that in real Bujutsu (martial arts [techniques]), one does not wait for the attacker to enter, but rather one should enter the opponent's attack. This application of osae and is the highest level of Kata application.
How does one reach this stage? Through Kata. How does one experience it? Practice Kata.