|“||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 spell to control his familiar, Sodom. 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 (other brands appear dark brown) 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".
He is completely dedicated to Yuki considering him more important than anything else in the world. In Yuki’s previous life, he was a woman named Yuzuki. Luka and Yuzuki fell in love which caused Luka to defect from the Demon King and ally himself with the Giou Clan. He won't tell Yuki of their previous relationship because he believes Yuki wants to forget everything from his past life. 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. Toko always tries to interact with Luka and hopefully break down the wall around his heart. When she confronted him about this, he told her not to tread lightly on other people’s affairs. This left Toko sad. Even after Yuki arrived she tried to help Luka by urging him to reveal his relationship with Yuzuki. He refuses and interrupts Toko when she tries to tell Yuki herself.
When Tsukumo was injured by Reiga, Toko vented to Luka but quickly said she needed to stay positive and set an example for the younger Zweilts. Luka told her that he wasn’t her comrade which greatly upset her. He went on to add that because he wasn’t her ally should could be weak around him. She quietly leaned against his back allowing herself to release her sadness.
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. Once Reiga commands Luze to protect Yuki, he begins to butt heads with Luka. They look like true siblings and amuse Yuki. They now have a casual competitive attitude over who gets to be near Yuki.
- "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."
"Yuki i love you"
- 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 is said to have a sweet scent and always smells good.
- He can change the length of his fingernails to extend to four inches long.
- Hotaru Odagiri didn’t want to make Luka too flawless so she gave him the habit of loving junk food. He’ll eat just about anything including Toko and Lia’s bad cooking