~With Kyoya~
"Fire Dragon's Sword Horn!!!!!!"
Kyoya engulfs his entire body in flames and then propels himself towards his corrupted copy at high speed, hitting him with a powerful headbutt. Afterwards, Kyoya proceeds to launch his copy into the air with a pillar of fire produced from his body. However, the copy quickly looked at the original as he landed on the ground.
"Ice Devil's Shiver!!!!"
The replica created an ice shard funnel that formed a straight line heading for Kyoya. Seeing this, Kyoya knew that he had to act quickly. However, he was sure of one thing, losing here is not an option.
"Fire Dragon's Iron Fist!!!!!!!"
Kyoya ignites his fist in flames and punched the ice shard into pieces. Afterwards, he got in front of his copy and punched his face as the copy was damaged by not only the blunt force but by the flames as well.
"So this is Dragon Slayer Magic...but if this is really Natsu's magic and it functions like my Devil Slayer magic, we'll just be at a stalemate by eating each others flames. While I want to master this new power, I also need to master my Devil Slayer Magic."
"Ice Devil's Fang!!!!!!"
The copy of Kyoya quickly clads his arms in ice and punched the real Kyoya in his chest. Afterwards, he launched a consecutive barrage of punches towards the mage which sent him flying backwards. As the copy ran towards Kyoya, the boy merely smiled.
"Fire Dragon's Crushing Fang!!!!!"
Kyoya ignites his fist and then swings it in an arc, striking his copy with his fingertips, leaving a flurry of flames in their wake. As the replica was engulfed in flames, Kyoya was thinking about everything that happened. His copy kept using his Devil Slayer Magic continuously, yet hasn't lost his sanity yet.
"Wait....there must have been something i've been doing wrong. Back when I fought Mard Geer and Invel, the markings might have already been on my body without my notice. But as soon as I did noticed, I panicked."
"Ice-Make:Silver!!!!!!!"
Summoning his Devil Slayer magic, the copy used it to boost his Ice-Make Magic. Gesturing with his right hand, the copy froze the humongous space in front of him along with the real Kyoya. As this happened, Kyoya was still thinking.
"Wait....my Devil Slayer Magic only lost control whenever I noticed the black markings and panicked. Is it possible, that my magic sensed my rejection and went haywire?"
As Kyoya thought to himself, the ice that imprisoned him shattered. He began to have an understanding of his Devil Slayer Magic. He shouldn't fight it when his body is starting to become demonized. No, if anything, he needed to accept it. His fear and hatred towards devils clouded his judgement so much, that he didn't even wish to rely on his only weapon against them.
"Alright, I think I get it. If I want to master Devil Slayer Magic, I shouldn't just focus on the characteristic that slays devils."
As Kyoya said this, he looked at his right arm. Soon he made the markings for his Devil Slayer Magic appear. As he did, he drew on more power from it as he made them grow on the left side if his body.
"What I should do is simple. I'll focus on the demonic properties of my magic."
As Kyoya said this, he forcefully made the black markings cover up the left half of his body, with the arm's black markings not being seen due to his bandages, as his left eye changed to the color red. The process when Devil Slayer Magic makes black markings spread across its users body.....when the black markings cover half of the user's body and causes their eye to change on whatever side is afflicted....that's when the process is at its peak. This process is known as "Demonized".
"This replica....i'll shatter it along with your past image of me Echidna, because i've already surpassed the image you have of me!"
Soon Kyoya created a giant axe sword from his Ice Devil Slayer Magic as he held it in with his left hand. As his copy got close to him, the copy suddenly stepped to the side as it avoided the axe sword since it was thrown at him. While this happened, Kyoya had quickly jumped high in the air.
"Ice Devil's Frozen Flower Funeral."
Using his Ice Devil Slayer Magic, Kyoya swung down his left hand, summoning a column of snow that fell down onto his copy. As the snow made contact with the copy, ice flowers sprout all over its body, instantly trapping it in a pillar of ice as the ice was constantly eating away at the copy's devilish mana. As this happened, Echidna had a smile on her face as she spoke to the ice mage.
"So you've realized what you needed to do to make your Devil Slayer Magic easier to control. You didn't need to reject it, but to accept every aspect of it, even the parts of it that you detest."
"I see. Thank you, Echidna. At least, I wish I was sincere about that, but you probably have more in store for me."
"Of course, you still have one more power you need to master. I have the perfect replica for you to face. After all, who else can teach you better than the one who introduced you to said magic."
As Echidna snapped her fingers, a large flame appeared before Kyoya. As the flames began to go down, Kyoya saw the figure beyond the veil of flames. Seeing the look on Kyoya's face, Echidna smiled as she explained the situation.
"This opponent is based off of your memory of them. This one should be able to help you figure out a way to utilize Fire Dragon Slayer Magic. Through this battle, try to find a way to harness it in a way only you can do. Make that magic your own. To do so, you may only use the Dragon Slayer Magic you received."
"I'll kill you.....Vanica!!!!!!!"
There he was, the etherious known as E.N.D, but Kyoya couldn't just see him as E.N.D anymore. He couldn't see him as a devil he needs to kill. As Kyoya ignites his own fists in flames, he unties the bandages around his left arm as he exposed the mark on it and looked at his opponent.
"Natsu, just hold on. I'll save you and the captains from the Dark Triad! No matter what!!!!"