Saya, a high-school student contending with amnesia, lives with her adopted family and maintains a typical daily routine. However, her unquenchable hunger sets her apart. While spending time at a park, she meets Hagi, a man on a long search for her. This unexpected encounter transforms her uneventful life forever.
Hagi, a charming young man, stirs a sense of familiarity within Saya, unlocking a part of her elusive memory. Being more than a mere human, Saya embodies an enigmatic persona with a primordial history. Her purpose is to pursue and exterminate the monstrous beings termed as Chiropterans.