Okay, so I have decided to write some about how I teach Kata Bunkai, this is a great place to start. This information comes from my own experiences, years of practice in Shotokan Karate and several other martial arts forms, some great instructors, seminars with other incredible martial arts instructors, and lots of books.
Stances form the foundation of movement or the transfer of energy. During the performance of kata a stance is essentially a snapshot of motion. As much as stances appear static they are not. There are no pauses in a fight and a kata's movements are supposed to mimic the movements of a fight. Stances are essentially the best possible position for your body to be in at the moment of energy delivery.
(To take that a step further, Aikido and Aikijutsu systems as one example use the same stances as Karate, as do all fighting styles really, just because the movements are natural even though they may not seem to be when you begin practicing them in earnest. I am working on a book that will be a better job of explaining this idea as it relates to the Aiki arts. Yes, this is a shameless plug!)
Another arguement I have heard over time is, where should the pressure of the stance be? Should I grip the ground with my feet? Should I pull in with my feet and press out with my thighs. Should I...blah blah blah. Honestly, this is all going to be true at some point or another. Stances should be mutable, adaptable. Fights are a mess. They rarely go the way you hope they would and no amount of planning will prepare you for the shock and chaos of the event. Okay, not entirely true but trust me when I say, if you have never been there before it will be eye opening.
So stances need to adjust to chaos, to be adaptable. Perhaps the stance needs to be narrow one moment and wide the next. Mobility and stability are inversely proportional in my opinion. The more stable you become the less mobile you are. Thus one stance could be either or a middle ground making you not particularly stable or mobile. In that case you would have stability and mobility in equal parts. Why does that matter? Throwing someone is going to require some stability or else you could go down with the person you throw. Could be okay in some cases but sometimes it is a VERY bad idea. Imagine a law enforcement officer going to the ground when surrounded by multiple assailants. Might very well be the last time he does that... He needs to focus on staying upright. In this case he might still be in a lot of trouble but if he is on the ground escape is not much of an option anymore.
So, find the purpose of the stance. Find ways to challenge the strength and integrity of the stance. Playing tug-o-war, sparring, hitting a heavy bag, and there are other alternatives to testing a stance too. I will list them some other time.
Next, the first move of Heian Nidan/Pinan Shodan.
Some other topics I want to cover:
Defensive conditioning taught in the Heian/Pinan series.
Application of Hikite.
Techniques hidden in your "Block".