A Chiropteran is a grotesque, undead monster with the ability to disguise itself as a human. It lives by feeding on peoples’ blood. There is a secret organization called the Red Shield that exists to hunt down the Chiropterans.

In the year 2005, Okinawan high school girl, Otonashi Saya, lives her life peacefully. She is normal in all respects, with the exception that she lost all her memories a year ago. However, her perfect life is about to change dramatically.

She meets Hagi, a man in a black suit playing a cello, who gives her a katana. At that moment, history turns a new page.

What secrets does her past hold? Will Saya remember?