Hyoudo Riki is just an ordinary guy who likes to wear a tiger mask while Kung Fu fighting, which means he fits in real well at BATTLE ROYAL HIGH SCHOOL! 
 
Unfortunately for Riki, he's the doppelganger in our world of Byoudo, Master of the Dark Realm, and when a dimension gate opens between the two worlds, the evil Fairy Master tricks Byoudo into making an attempt to conquer out beautiful, and better lit, world. 
 
Now poor Riki is semi-possessed by his opposite number, and the minions of the Fairy Master are mutating his classmates into hideous lustful monsters. To make matters worse, all the inter-dimensional commotion has attracted the attention of a sword-happy exorcist and the heroic Zankan of the Space-Time Police! 
 
Which all means that Riki is about to take one bitch of a mid-term. The course is survival, and forget "Pass/Fail." This test is graded "Live/Die!" 
 
(Source: AnimEigo)

Misaka