Whilst Awase is a commonly described and accepted skill in Aikido where its meaning is often accepted as 'blending' our school's emphasis is on the 'harmonising' aspect. Awase itself has many levels of skill. The lowest is body awase, next is ki awase, next is intent awase and last is spirit awase.
The lowest being tai no awase or body harmonising itself has multiple aspects that has to be trained. Typically, we start with te no awase or hand awase using grabs and strikes. Later we begin to touch on body awase where we learn to see gaps and fill it, and move uke's body using various parts of our body. After that we learn ashi no awase or stepping awase and last we learn to use skin awase. It sounds complicated but its not. It sounds easy but its not.
Having understood the theory behind Awase, it makes it all the more frustrating when you can really apply it well. In kihon training, awase can be practised in a variety of ways. The most dynamic would be to use shomenuchi. At Tai no awase level, we can apply a variation of ken no awase to receive uke's shomenuchi. We often do this by remaining in the line of attack. Extending kamae and sinking center is the beginning of applying this skill. Leading Ki and enshin also play a critical role. Done properly, uke's shomenuchi loses power, they lose balance and they'll stand on their toes unable to strike with the other hand. This is a wonder to see, but obviously irritatingly hard to do. Variations will be to add chushin into the element by using 'opening the door' method of blending. Another which is to me the hardest to do, would be step off line and attack uke's center without him being able to track you or you clash into him. The timing here is impeccable, your strike will touch his chushin comfortably as his strike lands at your original position. Done wrong, uke's strike will track you and we end up clashing hands.
Why start with shomenuchi you may ask. In fact most times we start with kamae to kamae. Nage tries to apply awase in 4 directions. In the beginning, atari is needed to ensure we have some energy to work with.
Now, this structure practice of awase is important and not very easy to do. Yet in the stages of learning Aiki, awase is the first step of many many steps. Not understanding it and not being able to do it well doesn't augur well to our progress. If awase is difficult, musubi would be 10x more difficult to understand.
After mastering awase, you should be able to use it in any situation. I'm far from understanding it let alone mastering it but it hasn't prevented me from 'playing' with it. Most times, I like to practice pushes that take uke's balance. Whilst this is not a fantastic display of skill, it does incorporate usage of awase and will eventually lead to a better understanding of ateru, even shuchu. Sensei has demonstrated a few times how he uses awase to block opponents strikes (straight punches or hooks). It inevitably causes uke to lose balance even though the block is very light, almost like taps even.
So, since I subscribe by the saying that he who waits for perfection, waits forever decided that its about time I put all this theory to practice. All in the name of training mind you, but applying it to fast strikes from my silat mates is not easy. Actually its near impossible. After constantly trying to take their center which is hard because of the way they stand and strike, in the end I resorted to a simple ikkyo which works incredibly well. Whilst we look at the technique as something so basic that most aikidokas know how to counter it, these guys have no idea what we were doing. So that sort of opened my eyes a bit. Little things we take for granted, may be bigger things to other people. Still, this has in now way diminish my desire to master awase and I will try again until I can succeed. Lastly, I like doing it outside of Aikido classes because the students don't really know what you're trying to do and are not likely to cooperate and the fact that they have no intention of letting themselves be beaten even in training.