The Image of the Trickster in Bleach
(particularly the SS arc)
Ah, tricksters. We've seen them in folktales or in stories plenty of times; anywhere from Loki (Norse mythology), to Jacob (Biblical/Hebrew Scriptures), to Anansi (Akan/Ashanti mythology), down to Bugs Bunny and even tales of the hacker/geek (WarGames/Hackers/Swordfish). He might not be the strongest candidate, he might not be well-dressed, might not even do that well in 'formal' evaluations of intelligence (like the formal schooling system, if applicable); he wins through cunning, through cleverness.
Now, it should be obvious to all Bleach fans that Aizen and Gin are examples of this. But why? Why did we think 'Gin's up to something' during the Soul Society arc? Why do we wonder about how far Aizen's Magnificent Bastardy will go, what his motives are - why is even the role of Aizen up for debate? We can't seem to decide whether, in the end, he's Magnificent and Evil or Misguided and Good. And in the context of shounen manga, what might this mean?
I. 'Fox-face' Gin
You know how Gin always has his eyes closed, smiling that little smile? The crucial term here is 'kitsune no me', variously translatable as 'fox-eyes' or 'fox-expression' or even 'fox-face'. It's been used in anime before to great effect; just see Slayers, or Fushigi Yuugi. These characters can be wise, can be helpful; in the same way, because of their particular expression, no one really knows what they're up to. It's a mask, and when 'kitsune no me' characters break the expression by opening their eyes, that's an immediate signal that Something Is Going Down. In anime, also, characters start off with this expression; and so the expression serves as a signal to the viewers. "This is kitsune-no-me - I need to watch what this character does carefully."
In Bleach, there is a definite motif of masks; Hollows have one, and this becomes even more important later on in the series. This expression is another mask, a more subtle mask because there is no paint, no ceramic, no bone to serve as a signal; therefore, arguably, 'kitsune no me' functions as an immediate analogy. Here is a more subtle mask; and in the grand moralizing tradition of shounen manga, it is the more subtle masks we must be on the lookout for, because it is much harder to figure out if it is a mask or not, or even the reason why it is there. The line between 'good guy' and 'bad guy' becomes blurred; it is no longer "Those with masks [Hollows] are bad, and we know how to deal with them".
And now to the even more subtle mask.
II. Glasses - and Aizen
Ah, glasses. Otherwise known as 'megane', like in 'meganekko'. Only this time it's Aizen wearing them.
Prior to meeting Aizen in Soul Society, we met Uryuu Ishida, another glasses-wearing guy. Ishida was questionable at first; he entered the series as a potential rival of Ichigo's, smartly dressed and with glasses. He was intelligent, yes; his glasses would do that eerie half-opaque glint thing every so often (those of you who have watched Neon Genesis Evangelion, or Hellsing: yes, same look).
But are these masks and what should we be searching for? Upon meeting Ishida, we learn that he's extremely intelligent, occasionally is the sense of reason, and somewhat keeps to himself. Ishida = soft-spoken intellectual.
Aizen = soft-spoken intellectual, at least on first glance - those are the visual cues we have. Gin seems a bit suspicious, because of that perpetual kitsune-no-me expression; Aizen just seems like he's fairly intelligent, at first, that he suspects Gin like we do, and so we first sympathize with him.
Clever little bugger, isn't he?
We learn that not only did Aizen have something up his sleeve, but that his power lies in illusion; his zanpakutou's name is even an idiom revealing illusionary qualities ("Kyouka Suigetsu - "Mirror Flower Water Moon"). With the help of Gin, he manages to throw suspicion off of himself, use mass hypnosis, create an illusionary corpse, among other things.
Illusions are often connected to kitsune - they are said to be able to create an entire realm in the space between a porch and the ground, for example, and stories of bewitched (often male) humans thinking they are having children, in a wonderful house, with a beautiful wife, often end with the wife being a kitsune, the house being a dirt cave, furniture being leaves or bones, and so on and so forth. 
Okay, the connection of Gin to kitsune should be obvious by now; he's sly, he has those foxy eyes. But what about Aizen? And how is this interesting?
Remember, this is a shounen manga. Shounen manga tends to teach things; lessons like "It's okay to rely on your friends", and "Things might look bad now, but you can get through it", and so on. What does Bleach teach, by using these characters?
Kitsune are known for masquerading as humans. It was not uncommon for a beautiful woman to be suspected, even as a compliment, of being a kitsune; but they could just as easily be maids and messengers as scholars or courtiers.  One never knew what their intentions were, so one had to be careful in dealing with them.
In these previous examples of Gin and Aizen's behavior, there is a common thread; these are models of behavior that are subtle, that forces the reader (and other characters) to wonder, think, and doubt. We start doubting what we see, what we hear said.
We even start doubting ourselves, our will, our own capacity to know.
And this seems to be the lesson, which is an interesting one for shounen manga; the lesson that not all is black and white, that there are serious problems with what we thought to be The Way of the World, The Framework, The Way Things Are. We have to continually re-evaluate not only our outlook on life, but ourselves, if we want to survive in reality and not be captivated by illusions.
 - A wonderful explication of this is in Kij Johnson's novel "The Fox Woman".
 - Some examples, including the example of Tamamo-no-Mae, can be found here: Foxtrot's Guide to Kitsune Lore.