The Breaking of Kyurem (ca. 2500 BC)
It was not long after Arceus adopted his two beloved children that he had his first glimpse of his own potential doom.
The three were, at the time, traveling westward across Greenland to expand their abilities with manipulating ice. The practice proved nearly fruitless for Dialga - his specialties lay much more within the elements of earth and metal - but Palkia found success in applying her knowledge of water to the domain of ice. And of course, Arceus had already mastered the elements of nature centuries ago.
Amid their travels, the three found themselves suddenly ambushed by a thundering blizzard.
Kyurem had grown exponentially in power over the last several centuries, and had approached the point that his power had nearly consumed him. He was perpetually surrounded by a violent blizzard of ice, lightning and fire that only ceased when he slept. For a time, the dragon gloried in his power and reveled in the fact that none could touch him. But soon, the creature realized that such power came at a price. He had become death itself, and had lost himself completely.
When Arceus led his children to the north, they beheld the edge of the storm before them and marveled. Palkia, with her limited experience with ice, could protect herself for a short time, but could not fly into the storm without severely endangering herself. Arceus took it upon himself to travel alone, and leave his children in safety farther south.
The Alpha, with the eighteen plates of power that he had thus far absorbed, was a frightening sight. With only a breath, he radiated a force of stillness that halted the winds and plasma near him, parting the storm like a sea, and walked straight toward Kyurem.
Kyurem turned his gaze furiously upon the Alpha. Though he was miserably sick with power, he still did not want that taken from him. He attacked the Alpha with a focused onslaught of three elements at once, aiming to kill as he had killed so many other creatures in his fifteen hundred years. Arceus defended the attacks deftly, but as he had not yet faced such a powerful foe in his life, he did sustain several injuries.
But more severe than his physical wounds was his mental shock.
Before Arceus was a monster, drunken with power. Arceus knew that this was a god who had absorbed more godhood than he could sustain, and it had destroyed the creature's mind. It had converted Kyurem's soul into nothing but destruction itself.
And it shook Arceus to his core.
Kyurem managed to knock a battered, singed Arceus into the Arctic Sea, and thought he had won the battle after all. The Alpha floated for a time in those icy waters, paralyzed by shock, struggling in indecision. It seemed impossible for Arceus to reason with this creature, even with his significantly developed psychic abilities. The dragon had gone truly mad. So it left the Alpha with a decision he never thought he would need to make: if he could not take this young god under his wing, as he had with Dialga and Palkia, would he have to kill him?
It was many minutes of icy silence, and Kyurem turned from the sea in satisfaction. An infant storm still sputtered weakly around him, and Kyurem felt that perhaps he would retire for the night.
The Alpha burst from the sea at that moment, erupting with a furious halo of elements that rotated around him like a globe. Kyurem prepared another onslaught of his own, though his strength was almost spent. Arceus bowed his head in apology, and, weeping, delivered every ounce of his power into the icy dragon's heart.
Kyurem's body shattered and his breath stopped, but he did not truly die. No immortal, once they absorb a piece of Arceus' shell, can die. We may fall into a centuries-long coma, perhaps, but we will not leave this mortal plane. Our very bodies could be burnt to a crisp, or split into pieces, but the plate bonded to our bloodstream will sustain our consciousness until the Alpha himself wills it to stop.
And so it was that Arceus approached the comatic dragon with a broken heart and a resolved mind. He pressed one hoof gingerly upon Kyurem's heart, and, breathing deeply, absorbed the power of plasma from him.
It assaulted Arceus with exquisite pain and exhilaration. He attempted to maintain his focus, but found his mind fraying at the edges. It was like a drug; addicting and overwhelming and delicious. He could not stop himself from absorbing the whole of it. Kyurem's body became a dead husk of icy flesh, and Arceus buried his corpse there under the snow of northern Greenland.
And he began the journey south to return to his children, surrounded by the crackle of static electricity and sparks of heat in the air.