yuichiroh was an orphan by th age of 9..two years later a deadly virus spread across Tokyo, so vampires took him and his family from the orphanage in until one day his best friend Mikaela has an escape plan, but Mikaela and the rest of yuichirohs family from the orphanage was killed and murdered by vampires so he had to run away. 

4 years later (age 16) he is a vampire hunter. And his friend Mikaela is vampire, but yuuichiro thought he was dead.