Very little is known about Haji before he comes to live with Saya and her father in there mansion. Hagi ( Haji) is Saya's first, and only living, chevalier. Also, Saya's lover. Haji maintains the look of a man in his early twenties, when in reality he has been alive since the late 1800s. In the year 1870, he was purchased by Amshel Goldsmith purchased the 12-year-old boy from his parents at the price of a loaf of bread. Haji was brought to the "Zoo" and introduced to Saya to first be a companion and later on in hopes that they would mate and create new specimens for Joel and his colleagues to study.When Haji was first introduced to Saya, his appearance was small in stature, accompanied by a gray outfit, blue tie and braided black hair. When he first met Saya, it seems they did not get along as she had been spoiled all her life. However, after spending time together in a barn to dry off from the rain, Haji began bonding with Saya after she learned of his plight. As the years went by, Haji was Saya's only friend at the Zoo as he grew to understand and love her. He admired Saya's dream of wanting to travel with him and her fencing sword to see the world. By the time he reached adulthood, he was taller than Saya (which annoyed her) and had changed the style of his hair to include a ponytail while he close black clothing to replace his former grey attire. While growing up in Joel's mansion, Haji became suspicious of Saya never aging along with Joel giving her blood to ingest and her quick healing ability. Finally, he questioned Joel about these peculiar traits. However, all Joel would tell Haji was that blood was necessary to Saya's survival. Haji was further confused as Saya had never lost a significant amount of blood to need a transfusion. 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 Hagi 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, Hagi 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. Hagi 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. Hagi also fights with a handful of silver daggers that he keeps on hand. As with most chevaliers, Hagi 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, Hagi 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 chiropteran since Saya injured it while going crazy from being forced awake decades ago in Vietnam. In the opening credits of the final season, Hagi is shown with wings, but he does not use them in the series until the forty-third episode. After Diva's death, Hagi 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 Hagi's arms. Saya reloads her sword with blood and is ready to fight him to protect Diva's babies. However, Hagi takes her sword and pushes her aside so she can escape while he impales Amshel himself. As Amshel crystallizes, he stabs Hagi through the chest and the ceiling collapses on them both. He tells Saya that he'll always love her. Saya screams his name before they leave. She believes he may be dead, but Kai reassures her that Hagi 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 Hagi's blue hair ribbon tied to it. Hagi is alive and he is watching from afar, waiting patiently for his love to awaken after her thirty year sleep. In the manga, Diva convinces Saya that Hagi is like the rest of her companions and should get rid of him. But when Saya sees that Hagi cut the thorns off the roses for her, she warms up to him. Unlike the anime, when Diva is set free, Hagi sees her and thinks it is Saya at first. Diva, jealous of Hagi being Saya's lover, kills him. Saya finds him, and Joel tells her that if she truly cannot live without him, then she should give him her blood. Although Hagi shows jealousy towards Kai in the anime, it is more obvious in the manga. He even pushes Kai into the helicopter, telling him that "Saya is my lover".

Saya's Welfare.