He is partly instrumental in Saya's "awakening" and his right arm is covered in bandages, hiding some Chiropteran features that he is unable to change back into human form. This might be due to trauma when Saya sliced his hand during the Vietnam incident. Haji first met Saya when he was a child of age 12 and was brought by Joel to be her companion and hopefully mate and create more specimens someday. At this time Saya was 43 although she doesn't appear to be since she stopped aging in 1863. He lived with her in Joel's mansion for many years. But one day he fell from a cliff in an attempt to pick a flower that Saya wanted as a present for Joel's birthday. Seeing him bleeding everywhere and not really understanding that people don't drink blood to remain healthy, Saya gave him her own blood. Thus she unwittingly turned him into her "Chevalier."
Since then, Haji's single wish is to protect Saya and fulfill her wishes. It is also revealed that unlike Saya who "created" him, Haji neither eats, sleeps, nor goes into long periods of hibernation.
(Source: Wikipedia)
