Rein was a knight from a respectable family, who had stumbled by the cabin Sierra Mikain was dwelling in, dying from severe wounds, having failed to protect the woman he served. Rein was the first man to be transformed into a vampire by Sierra following her encounter with the Moon Rune. Following this, Rein left for reasons unknown, although Sierra suspected he had left to avenge those who had wronged him.
Upon his return, the two were said to have become lovers. Together, they founded the Blue Moon Village, along with other people who had stumbled across the forest, seeking death, where they lived peacefully until Neclord stole the Moon Rune. Rein was one of the few vampires who chose not to die but to feed on humans to sustain himself. Following this, Sierra vowed to stop Rein, she being the one that gave him life in the first place.
Oh no, I'm dying. Time to be suddenly melancholic!
Rein survived until the Dunan Unification War when Nash Latkje and Sierra came across his mansion in the Dunan region. By this time, Rein had completely embraced his vampire nature and declared himself superior to humans. He fooled Sierra into thinking she had fatally wounded him and used the opportunity to feed on her, increasing his power. Nash was unable to harm him following this but managed to distract him long enough to rescue Sierra from his grasp, allowing her to destroy him once and for all.