Sonia Belmont is the protagonist of Castlevania Legends. At the age of seventeen she lived in a remote part of Transylvania. She was born with special abilities that allowed her to sense the presence of physical and spiritual beings, and was taught how to use a whip by her grandfather. It is not explicitly stated whether the whip she uses is Vampire Killer or not.
Within the castle, she encounters Alucard, the half-vampire son of Dracula. She had met him some time before and it can be inferred from their dialog that the two had formed a romantic relationship. Alucard was intent on dissuading Sonia from her goal, planning to stop his father alone. When Sonia would not yield, he challenged her to a battle to test her abilities. After she defeated him, Alucard was confident that Sonia could overcome Dracula and he went into a self-imposed sleep. Sonia defeated Dracula, and spared Europe from his evil influence for a time. Sometime after Dracula's defeat, Sonia bore a child who "would carry on the fate and tragedy of the Belmont family, and the bloodline of dark ways." The child would grow up to fight Dracula again and become a hero.
Source from Wikipeida