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.
Haji is Saya's first, and only living, chevalier. In 1870, the twelve year old boy is purchased by Joel and Amshel from his parents for a loaf of bread to be a companion for Saya, with hopes that they might mate and create more specimens for future experimentation. Haji lives with her in Joel's mansion for many years, he growing up but she never aging. In 1883, he falls from a cliff attempting to pick a flower that Saya wants as a present for Joel's birthday. Misunderstanding an earlier conversation between Haji and Joel about why Saya lives on blood, and wanting to save him, Saya feeds him some of her blood, unwittingly turning him into a chevalier. Saya feels some guilt over this through the years, but when she apologizes, Haji assures her that he has no regrets as it allows him to always be at her side while she lives her dream of traveling the world with her sword.
Haji plays the cello, a skill he learned from Saya. He usually carries his cello in a large black case that he can also use as a blunt weapon and a shield, and the case also holds Saya's sword. Haji also fights with a handful of silver daggers that he keeps on hand. As with most chevaliers, Haji doesn't need to eat or sleep, and he stays awake while Saya eats, sleeps, or goes into long periods of hibernation. Unlike Diva's chevaliers, Haji never makes a full transformation into a chiropteran form; however, this is by his own choice rather than a limitation of his power. He keeps his right hand bandaged most of the time to hide the fact that its form is permanently chiropractic since Saya injured it while going crazy from being forced awake decades ago in Vietnam. In the opening credits of the final season, Haji is shown with wings, but he does not use them in the series until the forty-third episode.
After Diva's death, Haji convinces Saya to live, confessing that he has always loved her. Agreeing that she does wish to live, Saya kisses him. As they, along with Kai and the rest of the Red Shield operatives, try to escape the opera house, Amshel attacks them, ripping off one of Haji's arms. Saya reloads her sword with blood and is ready to fight him to protect Diva's babies. However, Haji takes her sword and pushes her aside so she can escape while he impales Amshel himself. As Amshel crystallizes, he stabs Haji through the chest and the ceiling collapses on them both. Saya screams his name before they leave. She believes he may be dead, but Kai reassures her that Haji will return. Sometime after Saya goes into her hibernation, Kai brings Diva's daughters to visit the Miyagusuku crypt where Saya is sleeping. When they arrive, they find a fresh pink rose with Haji's blue hair ribbon tied to it.