horror

One day a gluttonous, average girl Saya forgot something at school and had to go back there during the night. Little did she know that two beings were waiting for her, a chiropteran and a handsome stranger, Hagi.

For some weird reason, Saya becomes entranced by Hagi and he offered his blood and a sword to her to beat the chiropteran. Gross, what just happened and why was she able to kill the chiropteran as if she was possessed?