Bloody Maiden: Juusanki no Shima

Onitsuka Miaki, freshman from Fujimigahara Girls’ Academy Naginata club, are going to remote island that owned by her captain, Igasaki Kotone, along with 11 members to do a training camp. Legends say that remote island is a place where the worst bandits lives and have national treasure beneath the island. Everything still normal before one of their member got killed. Their live-threatening experience begins now.
From Baka-Updates:
12 members of the Fujimigahara Girls’ Academy’s Naginata club arrive at a remote island belonging to the club president’s family. Legend has it that the remote island had long ago been the hideout of a group of extremely cruel bandits, and that priceless treasures – the fruits of their plunders – are still hidden somewhere on the island.
All is well until their club adviser and two members are brutally murdered. Thereby the curtain rises on the surviving girls’ life-threatening battle with a bizarre masked killer…