Miko

The Miko is the title given to the strongest Exorcist.

Summary
Rokuro's enchanted guardian is Abe No Semei. There is plenty of proof for this and most people already know this. Kuzonoa calls Rokuro Semei. An impurity calls Rokuro Semei (zemei)(happens in chapter 3). In chapter 9 Mayura in impurity form says Semei while looking at Rokuro. The seal on his chest when his guardian is released is Semei's seal.

Benio's enchanted guardian is the first basara Chinu. In chapter 28 we see a flashback where Shimon lists off the names of the basara, with images from the back of what they look like. If you count the images and match up the names to the ones we already know (Kamui, Higano and Hijirimaru) then you should see that the first basara Chinu has no image. Thats another reason why I believe that Benio's enchanted guardian is Chinu.

Rokuro's guardian represents yang and Benio's Yin. We can see this by the seals on their backs when their enchanted guardian is released. This leads me onto who the miko is.

Miko is and exorcist who has powers over both ying and yang. What Yuuto calls a true exorcist in chapter 14. The parents being the master of Yang (Semei) and the master of Yin (Chinu). The most powerful true exorcist will be born. I believe Arima is hiding this.

I think that Arima is hiding this because some exorcist would not agree with Chinu being an enchanted guardian and or the miko having power over yin.

Rokuro saw the Miko at ch 30 ant called it his child...

Trivia

 * It was revealed that the strongest Exorcist, the Miko, is the child of the Twin Star.
 * All of the Mikos are the reincarnations of one soul.
 * The Miko, as it looked when Arima Tsuchimikado was describing it, has striking similarities to the person Rokuro sees in a vision, who calls him its "child".