Reign of the Seven Spellblades, Vol. 2 (manga)

As night falls on Kimberly Magic Academy, the halls transform into a dark and deadly labyrinth... with Oliver and his friends still inside! Faced with a maze of evershifting passages and upperclassmen who hardly have their well-being in mind, the dark side of the school will test their mettle. However, even as they run from certain death, they have to stop Nanao from walking toward it. Just what mysteries does her fierce past hold...?