|“||Only I know your pain, your uncertainty, your loneliness. If we could be together forever, I'll say it as many times as you wish. I will never betray you.||”|
Luka has a dragon named Sodom as a familiar.
|“||His eyes are blades, and his hair the night. His shape and form are frightening and yet beautiful.||”|
As a Duras, Luka is one of the most beautiful classes of Demons, however, even amongst them, he stood out for his attractiveness.
Luka has pale, transparent skin, medium-length black hair and silvery eyes. He is tall with a slender but muscular build and has a red "brand zess" on his left shoulder. He also has a small claw shaped earring on his left ear which allows him to call on his weapon (much like the rings that the Zweilt use to call their demonbane weapons); ROXASS, a black sword. He also wears another earring on the helix of his left ear that's engraved with a control spell. He often dresses in a black coat and has a black cross around his neck, which was made and given to him by Yuki.
Although his real age is unknown, his appearance is that of a young adult.
Luka has an aloof and composed attitude, being pretty much indifferent to everyone but Yuki, to whom he is devoted. Although he is usually apathetic, when he becomes angry, his power flies up to levels that can be felt from far away. He doesn't trust anyone and likes to do things by himself, as towards the end of the anime, where he almost set off to fight Reiga (who had kidnapped Yuki) and his subordinates alone.
He was considered a slave because he was born into the Crosszeria clan (also known as the "Traitor Clan"), and that all the other Duras were intent on punishing the whole family and all its descendants for the crime of selling the names of 'his' brethen over to humans. For a duras, having your name known is the same as being enslaved. The demon king owned Luka, and as a symbol of this, he formed a permanent covenant by putting his own blood into Luka's Brand Zess, dying it red and causing Luka a great deal of pain during the process. Years later, Luka is still haunted by the memory and feels physically ill when recalling it. Because of the covenant, if Luka should ever betray the demon king, he would die, but he made a new contract with Yuki, nullifying his previous contract with the demon king. However, Luka hints that the prior contract with the demon king may not be completely nullified as long as his arm carries the "bloody cross".
The manga suggests a bit of a darker history. Luka tells Yuki he was considered a slave because he was born into the "sinner" clan, Crosszeria, and that all the other Duras were intent on punishing the whole family and all its descendants for their ancestor's sin. The demon king owned Luka, and as a symbol of their contract, put his own blood into Luka's brand. The demon king's blood made the brand on Luka's arm glow red, and it caused Luka a great deal of pain during the process. Years later, Luka is still haunted by the memory and feels physically ill when recalling it. Because it was a blood seal, if Luka should ever betray the demon king, he would die. Luka explains to the current incarnation of Yuki that since he made a new contract with Yuki, the previous contract with the demon king was voided, allowing Luka to live.
His relationship with Yuki is complicated. He is completely dedicated to Yuki considering him more important than anything else in the world. Yet he won't tell him of their relationship Yuki 's previous life (this is yet to be explained in the manga). It was during the last war when he changed sides to the Giou Clan, because he made contract with Yuki's previous life. But he left his position as the loyal servant of the demon king after meeting the present Yuki's previous life. It was during the previous battle that Luka met Yuki (when Yuki was still a girl) and they fell in love. Luka promises he will stay with Yuki as long as Yuki wants to.
Luka is wary of Takashiro and finds him unworthy of his trust, despite Takashiro's interest in protecting Yuki at all costs. When Yuki's well-being was being discussed outside the orphanage, Luka attacked Takashiro, just barely missing him on purpose. This is a clear example of the amount of agitation Takashiro causes Luka. A scene that was omitted from the anime, but is present in the manga is when Luka says "You piss me off" to Takashiro and then storms off.
Luka has a friendly relationship with Toko. Although he called her a "random girl" at first, not even telling her his real name, their friendship eventually strengthens. Toko is the Zweilt that Luka gets along with the most.
Luze is Luka's younger twin brother. They have no affection for each other and have only met a few times. Luze considers Luka to be a traitor that dishonered their family, and is willing to kill him to help achieve Reiga's goal. The brothers look almost exactly alike, the only differences being that Luze has longer hair and amethyst eyes.
- "When I fall in love...it's only one time."
- "...Yuki, are you alright?"
- “Once again, I swear to you… My life will be your shield and my body will be your sword. Until the day I die…”
- "An illusion is darkness. Those who cannot see the darkness cannot resist its sweet temptation and are stained black. Eventually, the darkness envelops the light controlling everything."
- He is able to control his body temperature.
- His two earrings are rather important. The fang-shaped one on the top has Sodom and Roxass (his sword) sealed within it. The one on the side is an ability controlling earring and is engraved with a control spell.
- Luka once wore a yukata in the manga but he said it made him feel uncomfortable and didn't like it.
- Luka's lucky charm (a black cross) made for him by Yuki has a different design from all the others, making it particularly special to Luka.
- His name means "Light."
- He has transparent skin.
- He is said to have a sweet scent and always smells good.