My Despicable Vampire Twin
Hikaru was a supposedly ordinary girl, (because her father was a pureblood but her mother was a vampire hunter) was sent to a school of monsters, Sakurami Vampire High. She always picks a fight with Nagi, an aristorcrat, rank C fire-wielder vampire, and has Hiroshi, her faternal twin, and Shiro Yuki Suzuki, her best friend since birth and an aristocrat, rank B water-wielder vampire
She and her twin doesn't know their father was a vampire and later finds out on her eighteenth birthday, though she's the only one who was born as a vampire and will possess the power her father has while her twin will live as a normal human and possesses the hunter's abilities from their mother
They later found out that they should marry each other in order to continue the Wakamiya bloodline that their father had failed to do. The twins later fall in love not realising that her rival and best friend had fallen for her brother.......... too?!