Note: My first time writing Castiel. Be gentle.
Sam crouched low on the warehouse floor, his view partially obscured by a row of large metal storage bins. Finding the Impala on its roof had kick-started his adrenaline, and he could barely contain his relief at finding his brother and their grizzled mentor upright and talking to Castiel and Raphael.
He needed to get closer to hear what they were actually saying. Before he could act on that plan, a wet, tearing sound rent the air. A splash of red shot over his head and a clump of what appeared to be brown flesh landed inches from his booted foot. When he peeked out again, Raphael was gone. A discarded angel blade slid handily across the floor towards his hiding place.
Sam caught a glimpse of his brother's face. It was full of terror. That's all the impetus Sam needed to grab the blade and move forward.
"You don't need this kind of juice anymore, Cas," Dean cautiously admonished the angel. "Get rid of it before it kills us all!" His brother's voice was trembling and deferential, a tone generally reserved for soothing stray dogs or calming down crazy people.
"You're just saying that because I won. Because you're afraid." Castiel took two swift steps in Dean's direction. "We're not family, Dean—"
Sam didn't wait to hear the rest. As soon as he saw the angel threatening his big brother, he charged and plunged the blade through Castiel's back.
And nothing happened.
Castiel effortlessly extracted the weapon and placed it on a nearby table. "I'm glad you made it, Sam, but the angel blade won't work—because I'm not an angel anymore. I'm your new God—a better one. So, you will bow down and profess your love unto me, your Lord. Or I shall destroy you."
Terrified, the only sound Sam could hear was his own racing heart. Dean's crestfallen face, drained of all color, met his eyes over Castiel's shoulder.
"On your knees, Sam," Castiel continued softly, stepping in his direction. "That's the most popular form of supplication. You did try to kill me. The least you can do is set a good example."
"Cas, don't! He's still messed up from the Cage. He didn't mean it," Dean lay a hand on Castiel's shoulder to halt his advance.
Castiel spun to face Dean and Bobby, glowering at them. Soundlessly both men collapsed to the floor, unconscious.
"Well now," Castiel remarked, "that's one way to have the world at my feet." He smiled, and that smile froze Sam's blood. "On. Your. Knees," Castiel removed his trench coat and loosened his tie. Sam felt his knees weakening on their own under Castiel's gaze and he dropped, against his will.
"Sam, Sam, Sam…" Castiel circled him slowly. "So eager to stab and stick things into others." Castiel let out a sinister chuckle. "I wonder if I might be able to find something to stick into you."