A brief description of the Nanatsu No Maken Ga Shihai Suru manga:
Spring. In the prestigious magic school of Kimberly, this year ushers in another wave of new students. Clothed in black robes with a white cane and sword strapped to the hip, within his chest he hides pride and a mission.
As the sakura flutter in full bloom, the budding magicians are welcomed by a parade of magic creatures. However, they were allowed only a moment of leisure. An underground labyrinth that swallows up students on whim, upperclassmen that resemble monsters, and a faction that opposes human rights for demi-humans. While trying to survive in an ominous and terrifying place with his companions, Oliver forms a connection with a single girl with a Japanese sword strapped to her hip, the samurai girl Nanao. The story where their two swords clash, begins now.