Saya was an ordinary girl, until one day she meets a monster and then her life changes. She steps into an endless war between the human beings and the Chiropterans. She enters a group which fight those bloody monsters and tries to prevent their actions. Saya has a special ability of killing those monsters, her blood is necessary. Therefore, with the help of her family, friends and other allies, she is going to fight.
Both series have the main character Saya fight with block sucking monsters that hunt people for their blood. Saya is using a katana as her main weapon to fight against them and she also has the ability to heal very fast.