The guy in the wall is Frau and he's the perverted bishop from the manga 07-Ghost by Amemiya Yuki and Ichihara Yukino.

Here's a little summary of it.

Barsburg Empire's Military Academy has always been known for training the elite with potential to become superb soldiers who won't bring shame to the name of the empire. The students of the special program freely utilize an ability called "zaiphon" to fight... Everyone's capabilities are different, and in many cases, reflect their nature. However, not everything is what it seems, and nothing will be the same for Teito Klein after passing the last exam...


If you want to check it out go to 07Ghost_awards and look for the link to the scanlations.