Date A Bullet: Dead or Bullet
This is the story of Tokisaki Kurumi that shouldn't have been told——
The amnesiac young girl, Empty, who woke up in the neighboring world encounters Tokisaki Kurumi. Led by her, the place she arrived at was the school's classroom. In order to kill each other, the girls known as semi-Spirits gathered. Now then——Let's begin our battle (date).
(Source: Date A Live Wiki)