Zero's younger twin brother. When Zero and Ichiru were both younger, they were both taught and looked after by Touga Yagari. Ichiru did not seem to share Zero's natural ability because he had a weak body and would get sick quite often. Zero and Ichiru were very close as children, though Ichiru claims to have hated Zero after overhearing that his parents preferred Zero as a hunter.
Ichiru had some involvement with Shizuka over the murder of his parents. He admired and deeply cared for Shizuka as she was the one who he says 'saved him from the depths of loneliness'. He acts as Shizuka's body guard, and in return Shizuka gives him her blood, which has cured him of his weak body. Although he wishes to become a vampire, Shizuka refuses to turn him into one.
When Shizuka died, Ichiru drank her blood before Zero was able to. As Ichiru disappears from this incident, he returns back to Cross Academy as a student, but revealed that he works for the senate.
After attacking Rido Kuran, in revenge for Shizuka, Rido severely wounds him. By this, Ichiru decides to shoot Zero, as this will trigger the thirst for blood. The reason being, Ichiru knows he is on the verge of dying from the loss of blood and wants Zero to devour the remainder of his life. By doing this, Zero would acquire the full amount of power that he should have had from birth. Ichiru's final wish is for Zero to live on and do what he himself couldn't accomplish.
What type of anime do you think twins most commonly appear in? Do they appear in high school romance comedy anime? It turns out that a lot of the most iconic anime twins show up in another genre entirely...