Saika Kuozaki was the principal of the Void Garden. Currently, she has passed down her identity and powers to Mushiki Kuga. ~!She transfered her conscience a backup body named Kuroe Karasuma.!~

Saika Kuozaki is an all-powerful witch with looks to die for. She's also the only woman who can thwart the mysterious entities attempting to destroy the world once every 300 hours. When Saika is mortally wounded, however, she bequeaths both her powers and body to the normal high school boy who happens upon her, Mushiki Kuga. But just because Mushiki has her abilities doesn't mean he can control them. To stand a chance of saving the world, he'll have to attend an academy for mages as Saika—all while keeping his identity under wraps!
 
(Source: Yen Press)

Saika Kuozaki is an all-powerful witch with looks to die for. She's also the only woman who can thwart the mysterious entities attempting to destroy the world once every 300 hours. When Saika is mortally wounded, however, she bequeaths both her powers and body to the normal high school boy who happens upon her, Mushiki Kuga. But just because Mushiki has her abilities doesn't mean he can control them. To stand a chance of saving the world, he'll have to attend an academy for mages as Saika—all while keeping his identity under wraps!
 
(Source: Yen Press) 
Note: includes an extra chapter.