Trinity Seven, Vol. 1: The Seven Magicians - manga (Trinity Seven, 1)

Arata Kasuga is living an ordinary life with his cousin, Hijiri, when a mysterious happening called a "Breakdown Phenomenon" makes her vanish before his very eyes. Determined to eradicate the Breakdown Phenomenon and get Hijiri back, Arata enrolls at Royal Biblia Academy. It's a tough road ahead, but nothing's impossible when you've got seven beautiful girls--each a master of her own magical art--by your side! The romantic comedy and sometimes-serious wizard school story begins!