Ichiru Kiryu

Ichiru Kiryu (錐生 壱縷, Kiryū Ichiru?) is Zero's younger twin brother. When they were younger, they were both taught by Toga Yagari to become vampire hunters. Ichiru, however did not seem to share Zero's natural ability and was often ill. Zero and Ichiru were very close as children, although later Ichiru claims to have hated Zero after overhearing that his parents preferred Zero over himself.

Shizuka Hio let Ichiru drink her blood to strengthen him and cure his chronic ill health, although she did not turn him into a vampire and he remains a human. He now attends Cross Academy as a Day Class student by the orders of Shiki's father, Rido Kuran (and by Zero's permission). It appears Rido has promised Ichiru that he will kill those who killed Shizuka, which is probably the main reason why Ichiru is working for Rido Kuran.

When Zero was locked up by the Vampire Hunters Association, Ichiru visits him and appears to have shot him due to hatred. However, it is revealed that Ichiru was terribly wounded because he tried to kill Rido, the person he was truly after because of his role in Shizuka's death. After he shoots his brother, he convinces Zero to drink his blood so they could finally become one as they were originally supposed to be. Ichiru stated that he was happy that he was not dead in Zero's heart and when they hug, he says that he feels comfortable to be in his arms, recalling a time when the brother's slept in the same bed often and were loved equally by their mother.After Ichiru's death, Zero appeared to grow vines, most likely from all of Shizuka Hio's blood that Ichiru has ingested