Ga-Rei-Zero

Ga-Rei: Zero is an anime only prequel to the Ga-Rei manga by Segawa Hajime serialised in Shounen Ace.

Will you kill someone you love because of love?

An elite squadron trained to combat supernatural forces is called in to investigate reports of invisible monsters terrorising Tokyo, but their mission is complicated by the interference of a rogue exorcist. When the mysterious female slaughters the overmatched attack force, her former comrades are ordered to lock down the crime scene – and forever silence their old friend.