At Dean's request, Cas started coming on cases. The angel noticed a little tension leave Sam's shoulders the first time Cas walked to the car as they headed out for a hunt. Castiel was glad to help give both of them some peace of mind.
Beyond the obvious worst-case insurance, an angel's powers often came in handy on just about any hunt, and Cas was happy to help with his limited grace wherever he could. He noticed his powers weakening, but the difference was slight, and it was yet to be a problem. He kept trying to find time to talk to Dean about it, but it never seemed like the right moment. So he put it off again and again, figuring eventually the time would come.
Dean for the most part kept it together. Castiel could see the struggle for control, but so far he was the one who came out on top. The price was recklessness. Too often would Dean let the fight last longer, let it draw out without drawing blood, or going for the kill. It was less violent, but on more than one occasion he had been a little too close to getting hurt.
After the first time Dean almost got his head torn off by a werewolf, Sam had chewed him out at the top of his lungs for nearly an hour. It didn't seem to slow Dean down. He'd throw himself into every fray, and take just as long dealing with it. Cas found himself worrying often, but for weeks he had always been fine.
The old house they were searching that day for the bones of one John Walter, angry spirit, was huge. Even so, Cas wasn't overly worried when they each took a different floor. He had watched Dean disappear up the stairs, and heard Sam head down to the basement as he began his sweep of the ground floor.
The crash and splintering of wood coupled with the grunt of pain from upstairs sent Cas running, only to be thrown back through a bookshelf himself. Before Cas even got the chance to right himself, the ghost was up in flames. The angel wasted no time pulling himself up and taking the steps two at a time to reach the room he heard Dean from. He froze in the doorway for just a moment before throwing himself to the hunter's side.
Dean meanwhile was curled in on himself, resting on his side, both arms clenched over his abdomen. The pool of blood spreading from him stood out against the light wooden floor, and began to soak into the edge of the dusty persian carpet in the center of the room. A large splintered table leg lay beside him, clearly what ripped through the hunter's flesh to create this wound. The salt gun was beside him, still loaded, and Cas could guess that he had been taunting the spirit, waiting until the last minute to take his shot. And he had gravely miscalculated.
Dean managed to look up, making eye contact with Cas who was looking more than a little worried. True to himself, Dean managed a toothy grin, though that only served to highlight the blood in his mouth. Cas found himself staring at it, leaking out the corner of his lips, coating his teeth, concentrated in the cracks. "Nice… of you to… join me." He panted, grimacing and losing the last push of bravado he had.
Castiel froze in place for a moment, rare for him. He was startled when Sam ran in the room behind him, having been drawn to the same sound. He regained his focus and slowly pushed Dean's hands out of the way pressing his palm to the rapidly spreading stain across his shirt. He tried to pool and push his grace forward, but nothing happened. He froze.
"Heal him." Sam knelt beside him, quietly begging the angel to save his brother.
Cas frowned in concentration, trying again, but still… nothing. He made eye contact with Dean, his expression warping into one near panic. "I can't." He pressed down harder, trying again to make it work. To make something happen.
"What do you mean you can't?" Sam breathed, sounding dangerously close to panicking himself.
"I…" Cas kept his hand pressed to the wound. "My grace… It won't…"
" 's okay." Dean tried to assure him, replacing one arm over his abdomen, the other squeezing the angel's arm. "Help… help me up…"
"Okay… okay…." Sam's voice was shaking, and he gathered up Dean's duffel, thrusting the shot guns into it, zipping it up. "Cas you-"
Castiel nodded, slipping one arm under Dean's, hefting the hunter up and close to him. Dean groaned in agony, beads of sweat lining his forehead as the pain of being moved coursed through him. Cas tried to ignore how little of his own weight Dean could hold, how his feet dragged with every step, how the blood made his grip so slick he had to readjust twice just to reach the stairs.
By the time they reached the car, Dean's breath was coming in wet gasps as blood coated his throat. Sam opened the back door to the Impala and Cas shifted, sliding in first and dragging Dean in after to rest across the angel's lap. Panic coursed through him with a strength he hadn't felt since he was human. He ran a hand down the side of Dean's face, silently begging him to be okay, trying to check him over.
Dean's eyes were dull, but he kept forcing himself to look up at Cas, catching his eyes, trying to somehow assure him it would be alright when he himself didn't know.
Cas put his hand flat against Dean's stomach again, ignoring the cry of pain, trying one last time to push any last drop of his grace into it, but he could feel it did nothing to the wound, and merely made his own head spin. Tears finally pushed their way past his defences, falling to mix with the blood spread below him. "I'm sorry."
Dean tried to speak, but he couldn't manage the breath to do so. Instead he held a trembling hand up and caught Cas' in his own, giving it one last squeeze before it went limp, and he sagged bonelessly across the angel's lap.
Cas held him close, trying to keep him steady as the impala lurched down the back roads, racing towards the nearest hospital. He held his hand over Dean's, keeping it pressed down on the wound, trying to hold as much blood in as possible.
For the first time in four years Cas sent a silent prayer, begging a father who never listened to spare this man.
He became aware of Sam screaming something back at him. "He's still alive." He finally managed to answer, surprised since he hadn't fully processed what Sam had been asking.
"We're almost there."
The impala barely screeched to a halt in front of the emergency room's revolving doors before Sam lept from the driver's seat, pulling open the back door and helping Cas pull the hunter out. Cas readjusted and took the hunter into his arms, his waning angelic strength still allowing him to carry Dean on his own. Sam helped get him inside, and a trauma team was already being paged to the front, ready to take him into the back.
As Sam reluctantly returned to the car to get it out of the fire lane, Cas was left in the front lobby, covered in blood, looking after the door where they had taken Dean, feeling utterly alone.
Hours passed, and a blur of doctors and surgeons that Cas barely paid attention to. Sam had said a few reassuring words to Cas, but he had tuned them out for the most part.
After surgery, Dean was put in a private room. Almost thirteen hours after they had arrived at the hospital, Cas found his mind wandering. Sam had fallen asleep in a reclining chair over an hour ago, leaving the angel with nothing to do but muse over his failings.
"When were you going to tell me your grace had gotten so bad?"
Dean's voice startled him and Castiel's eyes snapped up. He set his mouth in a line. "I wasn't."
"Are you okay?"
"I'm not the one in a hospital bed." Guilt laced through the angel's words.
"This time." Dean pulled a face. "But seriously… how bad is it?"
Cas took a deep breath. "Bad."
"What happens now?"
"I don't know."
Dean paused for a moment, considering. "You're dying aren't you?"
"Dean-"
"No, you are."
"I may be." Cas said at last. "But Gadreel has been keeping an eye out in the books at the bunker, see if there is some way to help the situation I find myself in."
"You should have told us." You should have told me.
"I did not wish to add to your stress while you would have little ability to help." He shook his head. "I never meant for it to put you in danger…"
Dean fell into silence, his eyes scrunching shut for a moment.
"I did not think you would survive that." Cas breathed.
"Barely winged me." Dean mumbled, finishing up with a grin.
"I am afraid taking me with you on missions is less effective than you had hoped."
"Why, because you couldn't heal me? Nah, you're fine."
"Without full powers I will be able to do little to assist should the need arise."
"You mean stopping me from going dark side?" Dean sighed. He watched the angel nod, and he let his gaze slip off to the side. "Still helps. Having you around. You and Sam… help to keep me grounded."
"Dean…"
Dean seemed to consider it for a moment. "I don't want you coming though."
Cas set his mouth again, feeling a renewed flash of guilt.
"I don't want you to get hurt either."
"I'll be fine." Cas hesitated before he reached up and wrapped his hand around Dean's. The hunter had withdrawn somewhat from displays of affection after that vulnerable night he held the blade. The angel looked over his pale features, thinking not for the first time about how young Dean looked…
"Quit starin'. People are gonna talk." Dean joked, giving a half smile as he struggled to remain conscious, not wanting to go back to sleep just yet.
"Dean I-"
"Stop saying you're sorry." Dean warned, giving him a flat stare when the angel seemed startled.
"How did-"
"You always make that stupid face right before you apologize again for nothing." Dean rolled his eyes. "Did you know today that your healing didn't work?"
"No but-"
"Then you have nothing to apologize for. And even if you did, then yeah, you should have told me. But not because of that, just because you should have let me help you. I was stupid, I had a clear shot, and I didn't take it. That isn't your fault."
Cas sighed, closing his eyes for a moment. He looked up when Dean squeezed his fingers. "I really didn't know what to do."
"You did fine."
"Gadreel should be able to heal you fully when we get you back to the bunker." Cas offered gently.
"Good. Not feeling much like sitting around waiting for this to heal on its own."
"You have to be more careful."
"Oh don't you start." Dean rolled his eyes. "I am already dreading the lecture I'm going to get from Sam about this. He paused. "But I will."
"You should sleep."
Dean sighed. "Yeah." He looked up at the angel. "You'll be here?"
"Of course."
Dean gave one last squeeze of the angel's hand, closing his eyes and before long, he finally gave in to sleep.