Although 14-year-old Ichika Asagiri's beloved grandmother has passed away, Ichika still cherishes her advice to always let her heart decide freely and without constraints when it comes to love. While returning to her room from the funeral, Ichika spots a strange but beautiful girl in the yard. The girl, Aria, appears to be no older than Ichika and claims to be a friend of Ichika's late grandmother. Despite having a lot of questions, Ichika quickly joins Aria in searching for an unspoken item, only for the girl to inexplicably disappear when Ichika's mother walks in.

Ichika is left bewildered, but Aria soon reappears to request her help once again. Aria's actions grow stranger—from hypnotizing Ichika's mother to brutalizing a home invader—until her secret is finally revealed. As Aria leans in to bite her neck, Ichika realizes not only that this mysterious girl is a vampire but also that, for the first time in her life, Ichika is in love.