The Kiryus (Zero and Ichiru's parents)

They were Zero and Ichiru's parents and were also Vampire Hunters They were murdered by Shizuka Hio in revenge of killing her ex-human vampire lover.

Character concept
Neither their faces nor names have been revealed and are only featured very lightly. In the light novels, they are merely referred to as "Zero's mother or father."

Appearance
The father bears a striking resemblance to Zero and Ichiru in terms of hair and skin coloring. The mother has long blondish-brown hair tied in a low ponytail. Their father has the same hair color as Zero and Ichiru, silver.

History
Both Kiryus are high-ranking Vampire Hunters, and are the parents of Zero and Ichiru Kiryu. Despite loving both their sons dearly, the Kiryus felt Ichiru's illness and lack of natural talent in comparison to Zero would prevent him from becoming a Hunter. For this reason, they focused more of their time on developing Zero's skills as a Hunter, giving Ichiru the impression they favored Zero over him. Ichiru's resentment over his parents' seemingly preferential treatment of his brother would have tragic consequences later on and lead to the destruction of the Kiryu family. These events would be set in motion the night the Kiryus were assigned to kill an ex-human vampire who they'd been told had fallen to Level E. Unfortunately, the Kiryus were lied to and had been used as pawns by Rido Kuran to kill the ex-human vampire who had become his fiancée, Shizuka Hio's lover. Shizuka's grief over the death of her lover would drive her to insanity, and later, to revenge. With the assistance of Ichiru, who had become captivated by her, Shizuka killed both Kiryu's, bit Zero, and took Ichiru away.

Trivia

 * Zero's mother is the first female Hunter who appears in the manga.