Seraph of the End: Guren Ichinose: Catastrophe at Sixteen (manga) 6

Prequel to the hit manga series, Seraph of the End! Detailing the events before the apocalypse, 15 year old Guren Ichinose enrolls at Daiichi Shibuya High, a magical training school. Witness his trials as he must hide his true strength even as he is trampled on at a school for the insufferably privileged.