Castiel had lost his mind from grief. For three days and nights he had wept nonstop and would not pull himself away from his beloved's lifeless body. When his body would become exhausted, he'd just lie under the oak and fall asleep with his arms wrapped around Dean, as if his body warmth could bring Dean back to life. No kind words or condolences could make his heart feel any better, the loss was so immense.
Nature saddened around him. The trees lowered their branches, no flowers blossomed, the birds did not sing joyfully. The forest spirits grieved Dean's death.
Castiel had lost his voice from grief and mourning.
"Why did you leave me, Dean, why?" his lips were whispering soundlessly.
On the dawn of the fourth day, Castiel was woken up from his dreamless slumber by a stranger's voice, who was calling him by his name.
The lake spirit sat up and rubbed his swollen eyes from crying. A stern faced man stood in front of him with a golden tiara on his head.
"Castiel…" the stranger addressed to him. His mighty voice echoed in the depth of the forest.
The lake spirit startled when he recognized Hades – the god of the underworld.
"Your cries and pleas have reached me," Hades continued.
The fairy creatures hurried away into the depths of the forest. Hades' appearance always caused chills, even amongst the Olympian gods.
"I remember kindness from your ancestors. In difficulties, they always helped me to hide in your lake. I do not forget kindness and can return it for you in a favor. I can help you." For a second, there was a sparkle of sympathy in Hades' black eyes.
Castiel's eyes watered and he stared at the god pleadingly.
"Can you give Dean back to me?" sounded Castiel's voice, barely audible.
"I can. But you will have to make a sacrifice. This is the rule and even us, the gods, cannot break it." Hades looked down at the ground.
"Sacrifice?" repeated Castiel. "I am ready to make any sacrifice just to have him back. But what can I give you? What do I have?" Tears rolled down the spirit's cheeks.
Hades' eyes stared at Castiel piercingly. The poor spirit shuddered under the power of the god's gaze. "Your immortality," the words sounded ominously.
Castiel paled and gulped loudly. He closed his eyes and held his breath. After a while, he opened them and spoke with determination.
"Take it. You can take it right now, just give him back to me."
Hades let out a small, sad laugh. "But remember, you will never be able to return to the lake, as you will be a mere mortal. Do you understand me?" The god waited for an answer.
Castiel nodded. He had made the final decision. "I know. Bring Dean back."
Hades shook his head and sighed. "Only love can make a person do reckless things." The ruler of the underworld smiled sadly and approached Castiel.
A scream from unbearable pain became trapped in Castiel's throat when Hades' hand went through his chest. The blinding, white pain clouded the spirit's mind. Castiel could feel how the ruthless hand was tearing bit by bit the piece of his soul. The torture was insufferable and Castiel's exhausted body fell down on the green grass, unconscious…
Someone was gently slapping him in the face. As soon as Castiel opened his eyes, he saw a scared, familiar, and beloved face. "Dean…" he moaned and smiled blissfully.
"Cas, what have you done? Why have you done it? I was dead, but still I could hear every word down there. You, little fool. My little fool…" Dean was holding his beloved into a tight embrace and wiping his own tears off.
"You are alive." Castiel's fingers lovingly were caressing the shepherd's face.
"Yes, Cas, I'm alive." Dean was kissing his now mortal beloved's face.
Hades could not be seen anywhere. Probably he had returned to his realm.
The fairy creatures came out of the forest's depth and approached the couple.
"You cannot go back to the village. The black plague is still there. Castiel cannot go back to the lake either. He's mortal now," one of the dryads began.
"Stay here, with us. We will help you to build a house. No disease can enter this forest, the gods are protecting it," a nymph finished her friend's offer.
"What about my goats? They are left in the village. I locked them with some food and water when disease started to kill people, but they must be starving by now." Dean saddened at the thought.
"Do not worry about them. I will go right now and bring them back to you." A red bearded centaur, the one who volunteered earlier to take Castiel to the village, put his comforting hand on the shepherd's shoulder.
Dean and Castiel looked at each other and gave their consent to the fairy creatures.
With the help of their friends, Dean and Castiel built a small house and settled down in the forest. Every evening they would sit down and play their flutes. The fairy creatures laughed and danced happily to the merry melodies while Dean's goats jumped and bleated around them.
At the lake shore, on the spot where Castiel had been mourning Dean's death and his bitter tears dropped, the most beautiful willow tree grew as the sign of their purest love.