Hagi

Hagi (ハジ Hajiundefined) is Saya's first, and only living, chevalier.

Plot
In 1870, Hagi was 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.   Hagi lives with her in Joel's mansion for many years, him growing up but her 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 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.

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.

Abilities/ Powers
Hagi plays the cello, a skill he learned from Saya and later surpassed his teacher. He usually carries his cello in a large black case.

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. 

Weapon
Hagi uses the cello-case as a blunt weapon and a shield, and the case also holds Saya's sword. He also fights with a handful of silver daggers that he keeps on hand.