Personally I Like the Disease (Deanmon X Leviacas) (Destiel)

Prologue: Broken to Damnation

The greatest hunter of them all. The strongest fighter but the broken lover. These were names they called him before. Monsters feared him because of his past, but now even the good ones were fearful too. His brother, Sam Winchester, swore he would keep trying and always be there for him. He hasn't gone any further past the deathbed that changed his brother. Even Sam has lost strength to fix him, Dean Winchester, the King of Hell.

The search for the renewed king with the broken past brought the greatest fear to the angels. There was only one angel, the best in the garrison, who had never feared him. That poor winged soldier had been shattered by all that happened after he pulled the righteous man from perdition. Castiel, that was his name, never seemed to follow the rules when it came to the Winchester's safety. This time everyone was sure he had crossed all boundaries.

Castiel was out to save Dean Winchester and he would stop at nothing to do so. He would not allow Sam to put himself in the line of danger. Sam had asked him many times as to why he made such a decision. The truth laid deep within Castiel's being and six words he had uttered not long ago to Dean.

All the research from the books in the bunker, the searches on the internet by the younger Winchester,and the celestial knowledge collected by the angel led to one conclusion. They would need to be stronger than Dean to stop him from putting himself and others in danger. Castiel was the only one out of the two that could handle such large quantities of power.

They needed souls and many of them. When Cas' plans reached to heaven, he was rejected any entry. Even by his loyal friend, Hannah. He couldn't ask for souls from hell. Dean would figure out their plan in no time. The king of hell could and would do anything. Crowley may have been of use if he weren't Dean's foot stool at the moment.

Cas was left with no option other than the worst. Purgatory. Home of the worst. Afterlife of the monsters. Worst of all, prison to creations first beasts. They were written in history to be ferociously hungry. This wasn't normal hunger. It was hunger for power, death of nations, and souls. They were the leviathans. Castiel had always believed they were a myth. Just a scary story the archangels would tell to scare the fledglings. Unfortunately, now he could feel them and their venom in every inch of his form.