Re: Muga?
Continuing on with the 2nd Door...
Saiki Kanpatsu no Kiwami (Pinnacle of Great Wisdom)
The name Saiki Kanpatsu can also be read as "a flash of brilliance". 40.5 describes it as allowing one to "instantly predict the flow of the game". It's been quite a while since reading those chapters, but if I recall correctly, Chitose achieved this after years of research into Muga and thus this seems to be achieved through intellectual endeavors. This seems safe to assume since Tezuka is definitely the kind of person that is an intellectual, which would explain how he achieved the state. This technique seems to be limited by the number of variables in a match. For example, it cannot be used in doubles as that requires you to predict twice as many people. I have a small inkling that this may only be able to "evolve" in a sense to include doubles if the user's brain can learn to cope with the information overload. As this is a "brainy" technique, it would seem it should only be limited by the brain's capacity. This is only my theory of course.
Furthermore, Sanada's "In" which works by sending mixed signals to someone's prediction screws it up because one cannot ascertain Sanada's true intent. This would then mean that Saiki would be susceptible to Atobe's World of Ice as well since that takes place in a frozen instance of time.
Saiki is essentially the opposite to Hyakuren. Where as Hyakuren deals with a person's mastery of his physique, Saiki deals with a person's mastery of his mind.
Now to go reread the last volume to come up with the Ten'imuhou theory.
So the final door....
Ten'imuhou no Kiwami (Pinnacle of Perfection)
Early on Chitose believes Kintarou to have been the closest to achieving this. I honestly have to agree with him at that point in the manga even after learning how it is achieved. I see the key to achieving it as attaining a state of mind. It is attaining the perfect attitude for playing tennis. If Hyakuren is the embodiment of the physical aspect of tennis and Saiki, the embodiment of the mental powers of tennis, then Ten'imuhou is the attainment of the perfect attitude. Nanjirou doesnt says Ten'imuhou doesn't exist in that the attitude is what everyone begins with. I mean obviously it exists and it does amazing things, but I think what Nanjirou was emphasizing was that despite all it's abilities, the most important thing was bringing you back to that joy and happiness of being able to play. That desire to want to play just to play.
I see it as attitude makes everything. I mean what's the point of being able to do something if you don't enjoy it? Muga essentially takes you out of the game. Hyakuren is tiring and over works you. Saiki is basically studying and reading too much into stuff. Ten'imuhou however is having fun and that is what ties everything together and makes the ability.
As for what Ten'imuhou does? I think it'll probably be explained more in depth int he new series when we finally get to see more Ryoma. So far it seems to give you super abilities like serving so fast only a camera can catch it and to scare Yukimura. Other than that, we don't really know much about what it really does except make you the perfect player.
Anyhow that ends my theory on all aspects of Muga. I may append things as time goes on, but that's how I see everything right now.