Ayaka, my OC in Hellsing university

It would be a universe where my original character would be in Hellsing : She is reportedly a former university student who would do anything to save her recovering younger sister. But her sister is the victim of an incident caused by a vampire, who bit her. However, Ayaka would have fallen into the wrong place at the wrong time, as she saw a panicked crowd fleeing a horde of ghouls. She was attacked by a vampire who tried to bite her, but saved by a mysterious figure who shot her, and the bullet went right through to the heart of the vampire who is holding her hostage... and she gets bitten by the mysterious man, until the day she is found by the Hellsing Foundation following a missing blood bag from that bank, which the foundation paid for the delivery of the bags. Ayaka's goal is to save her sister, as well as humanity.