In the first one, anyway, while he annihilates all the councils, he cannot even come near to the Emperor and his siblings.
In the second one, instead, nearly in the end of his journey and became aware of his endless and unavoidable run in the karmic cycle, in the moment he breaks this infinity (which is the well-known mathematic symbol of “eight turned horizontally”) he can face finally the karma.
Another confirm about the role of the Emperor is shown when his siblings/guards die. In fact they become a caterpillar and a butterfly and behind them appears images of a blooming and the moon. The moon is the symbol of the "passing of time" because in the East the calendar (like formerly in the West) is lunar, while butterflies, caterpillar e blooming represent the endless life cycle of birth and death of all the living creatures. Hence broken the Time and the Life, or rather what Izo wanted to escape from, he can face the Karma. But a simple single breath throws Izo away: because Karma is the only ruler of the universe and no one can resist it.

However there are many other symbols and characters that appear in the movie. Izo in his journey does nothing but overtake all lives and times in a sort of Inframundus (a space between a netherworld and the real life) where there's no gap between space and time. It is the level where the cursed souls live, a place for the ones who have to pay for a punishment or who await reincarnation. It is also the level of demons and Gods, and so of who keeps the balance of the universe.
That's the reason why people of the past appear in the present and vice versa. That's also the reason why the living doesn't interfere with Izo and his contenders: because they are crossing the same space without living on the same level.
That's somewhat like the common belief of ghosts that live in their sphere, unseen by mankind but perceiving human actions in a distorted way.
How can we tell that Izo indeed gets in touch only with the deads and Gods/demons? The most explicit scene is when we found Izo weeping in the jizo cemetery of children. These are cemeteries where mothers who abort place a little jizo statue in memory of the child never born. Just in that place we find an old man (maybe a sort of protector) and some children that are wondering why Izo is so sad. The children, never born, and so free from the karmic pass, don’t know what is pain and the old man tells them the story.
Also Izo's lover, a prostitute when she was alive, is clearly a wandering spirit: like almost an Oni demon. She could free herself from the curse only killing Izo, but she fails.
Many monsters and phantoms are in a questionable placing, like the customer vampires, but is more likely an intent to combine old and new torments in order to create a universal nightmare feeling.

Mothers' figures are crucial. In Izo there are three, all with a different appearance, attitude and role. The first mother who appears as a sort of primitive goddess, voluptuousness incarnate and surrounded by candles, she copulates with Izo to have more children. She tells to be the mother of all, she's possibly the personification of maternity and birth, who lives eternally in the pain to copulate and give birth.
The second mother is the spinner, which mercilessly, after praying Izo not to go away, is chopped in half. The spinner, old and lonesome, is the exact opposite of the first mother, because she's the one who can chop off the thread of life as Karma wishes (that's just like in Millennium Actress by Kon Satoshi, the spinner is the personification of death). All these creatures are indeed sent by the “Council” presided by the Emperor to interrupt Izo's journey.
The third mother instead is the conscience. She's the one who'll give birth to a creature of light. She tells that she never met Izo before, because Izo in the past lived only following brutal instincts, but is only with the consciousness that he can understand his torment. The creature of light could, forcedly, be accosted to the concept of buddhist illumination, but seeing the destruction of all political and religious precepts, is more likely that only with the conscience can comes to light a pure and conscious creature. A very complicate figure is the black monk. He survived all the destructions of religion and is freed by Izo with death. I think his role is important for a matter of "spoken". In that situation takes place a discussion about what Izo is really searching and is reading, because the actor speaks with subtitles, that the viewer stores better some data that could be evanescent if coming from a sonorous source. So the liberation of the monk is a deliverance from the punishment of a condition of eternal musing, maybe because he's guilty, that has no more sense to be paid for because Izo shattered all the bases of religion.

There is a scene that many of you probably ignored but that's of extreme importance. If you notice, Izo kills anyone who stands before him, also who prays for mercy. Only two people are not shattered by his fury, except the ones not belonging to the terrestrial dimension (like the teacher in the school): they are the two poor farmers, which we see working hard and then eat a mere dinner. In fact they are incorrupt, by both politics and religion, as much as Izo is subject by the karmic cycle they are subject by the cycle of seasons. So they are innocent because they have no bounds with what Izo has to destroy: the secular power and the spiritual power.

A mysterious figure, but constantly present, is the "singer". For the whole we listen to his songs about stories of life but mainly on the meaning of life. These sequences are in fact intervals between each massacre made by Izo but they are not out of the narration but they accompany it.
I found this singer to be a sort of common conscience, maybe a spirit guide, which has nothing to do with Izo's conscience, represented by the woman. These intervals are nevertheless necessary because of the fast narration and also to make us think about various themes of joy and sorrow. Seeing that they'll be resumed in the ending credits but with a different way…

Many other aspects have to be analyzed, surely with some other views. Anyway with a single view these are the main aspects that can appear.
Speaking with someone else, however, I discovered a lot of different points of view, also like the christian idea of death and infernal punishment, which I have never considered, ‘cause that isn’t my main way of thinking.
Maybe, in the end, it would be nice to ask directly mr. Miike about the real meaning of this movie. Do we really need it? Isn’t it beautiful to have a movie so exciting, with so many possible points of view, as many as the lives that Karma should give us?

Translated by Riki Fudoh & Ameonna. Original version by Ameonna&Chaoszilla