This Night & This Road We're On by cordeliadelayne (both NC-17)

[onehoureternity.livejournal.com]

Fandom: SUPERNATURAL
Pairing: Castiel/Ruby
Length: 2,302
Author on LJ: cordeliadelayne
Author Website: Fic tag
Why this must be read: Castiel wants to know what it's like to feel. Ruby shows him. I love the forbidden feeling throughout the whole thing, like you're not supposed to be watching something that isn't supposed to be happening. Castiel desperately wants feel, and that's captured beautifully. Spoilers for 4.10

This Night

And it's sequel! This Road We're On (Spoilers for all aired S4 episodes, also Castiel/Ruby NC-17)