Tsukune was not, in fact, a vampire. Once, he had been a human, and then he had been turned. He had learned from masters of the art of fighting, and through determination and talent, had soon become one of his world's most powerful vampires, fighting for equality between humans and monsters. However, after he had absorbed the power of the great demon Alucard, and through him every creature on his homeworld, he had become more than that. Taking the vampiric regeneration to the extreme, each of his cells almost instantly adapted to anything, allowing him to mimic almost any genetic power, instantly regenerating from wounds, and changing the material of his body. Every one of his cells was a mutation center, capable of growing into an entire new body within minutes. While normal vampire blood had the power to change a human, the blood of the one known as the Ghoul God was a billion times more powerful. A single cell would corrupt the host body, break it down to it's most base components while preserving the DNA, and then return it to Tsukune for absorption.

Through the symbolic offering of his blood, however, no true change had been made. Tsukune had been reduced to nothing but a soul when every cell in his body had been simultaneously destroyed by the power of the Ka-Gash. Instead, the offer of blood was but a metaphor for a spiritual link, as Tsukune's soul bonded with that of Mithias, granting him access to the vast knowledge of the Demon Arts that Tsukune had proccured. Techniques to harness the inner power of all monsters to an extreme degree, and the Yokai Energy to back it up. It was not complete, of course, as the souls did not merge, but Mithias was granted at least some of the Ghoul God's abilities, including the ability to regenerate wounds that would be instantly lethal to any other being. Tsukune's power, Infinite Regeneration, made him effectively immortal to any attack that didn't directly target the soul.

"Let us see what you will fight for, Mithias Vladomere, vampire hunter. Let us see whether you can stand before the hordes of evil in this world, and wipe out that which corrupts and destroys all. The storm will come, and it will break you. But if you are truly just to your ideals, you will continue even broken, even when shattered, when the Lord of Insanity himself tears at your mind and rips open your body." Tsukune's voice is that of a man true to his convictions, and yet filled with regret and sorrow. "Let us see whether you can succeed where I failed." Heat flows through your body, as your pyrokinesis is boosted to unheard of levels, gaining the strength of the Kitsune. Fox Fire, capable of burning through steel and stone. 
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Stein grinned. Two scalpels were held in his bloody hands, as his eyes widened. He had been busy, of course, but even in a different timeline, he had felt it resonating in his very soul. He had sensed the sheer change in the future, the power that had arisen from death. Could it be? Tsukune, who had once stood against Stein, had died, and yet this was clearly his soul he could sense. And the other vampire. It seemed he had been right, when he first met the vampire in Hell's Coffee Lounge. Another player had been added to the game, and they were already meeting the greats.

Stein would find Mithias, and break him. He would shatter his ideals, and watch his mind bleed. He would rip everything he loved to pieces before his eyes, and force feed him the remains. He would rip throug his soul not with any power of magic or wonder, but with the sheer realisation that all his ideals were but dirt before the harsh reality and cruelty of death and pain.

Mithias would fall.