Gleipnir 12 (manga)

Elena, Naoto, and Aiko’s little sister Hanabi aim to finish the battle and save the world by destroying the frightening entity in Honoka’s form. The prospects seem grim, but the world will disappear whether the three run or meet their end in battle, so they’ve got nothing left to lose. Honoka was their friend once, and although the creature that wears her face can hardly be called human, none of them is human anymore, either. The only question is, which monster will be left standing when the dust settles?