Zero & Ichiru

Kiriyuu Ichiru (錐生壱縷), Zero's younge brother was too trained by Toga to be a Vampire Hunter like his parents. However, unlike Zero and his prodigy abilities, Ichiru was sickly and weak, which made Zero worry over him endlessly. One night, he overheard his parents saying that they didn't know what to do with Ichiru because he wasn't suited to be a fighter, not like Zero. Though Zero loved his brother very much, Ichiru began to resent Zero and his parents. After hearing what his parents said, Ichiru ran outside and met a crying Shizuka, who sat in a tree mourning her dead lover. In his pain, his confusion, and his anger, Ichiru connected with Shizuka.

After the death of his parents, Ichiru became a loyal servant to Shizuka. His hatred for Zero only festered, so much so that he tossed to Shizuka a sword with which to kill Zero. Ichiru wants Zero dead, that much is true. He still resents Zero for the fact that his parents didn't hold him in the same regard as they did Zero.

After Shizuka is killed, Ichiru vanishes for a time only to reappear as a student at the Academy in chapter 30. He is, of course, immediately popular in the school.

Ichiru becomes loyal to the enemies and even goes so far as to drink the vial of Shizuka's blood that Kaname had saved in order to keep Zero from getting it and returning to his human form.