Castiel remembers when he discovered he liked kisses. Well, not kisses, really. He happened to feel rather uncomfortable whenever anyone got too close. Unless it was Dean.
The first time it happened, it was the night the angels fell. When Castiel had finally found Dean and Sam, he had collapsed at their feet. They had carried his shivering body into the Batcave. As Sam ran to get blankets, Dean wrapped his arms around the ex-angel, trying to warm him up.
"Don't worry," he muttered, rubbing Cas briskly to get his blood flowing again. "We'll get you warmed up." Without even seeming to be aware of his actions, Dean had planted a light kiss in Cas's hair. Cas had been fading in and out of consciousness, so the action might have even been in his imagination. It felt nice nonetheless.
The next time, Cas had gotten hurt on a hunt. He still wasn't used to the fact that he couldn't heal himself magically. He had sustained a pretty bad cut on his forehead, so Dean took him home and patched him up while Sam finished the hunt.
"It hurts," Castiel whined as Dean stitched up his forehead.
"So be more careful next time," Dean responded as he tied off the suture.
"Make it feel better," Cas pouted. "Please, Dean."
Dean sighed. "What do you want me to do?"
"I don't know. What did your mother do to make you feel better when you got hurt?" Castiel asked.
Dean turned bright red. "I swear," he muttered through his teeth, "if you tell Sammy about this I'll kill you." And, still blushing furiously, he leaned forward and kissed the stitches lightly.
"Better?" he asked, still bright red and resolutely avoiding Cas's eyes.
"Yes, actually," Cas responds, somewhat shocked as a light feeling spreads through him.
And so it becomes a ritual between them. Every time Castiel hurts himself in some way, (and that happens more often than not- he didn't just lose being an angel when they took away his grace, if you know what I mean), Dean patches him up and kisses the injury. And every time, Castiel enjoys the kiss. He becomes less and less careful. That's not to say that he's becoming reckless and purposely endangering himself, because he isn't. He's just not taking extreme care to avoid injury.
When he cooks, he moves too quickly and burns his hand on the stove. And so, Dean kisses his hand.
When he goes for runs, he doesn't watch where he's going and stumbles and falls. And so, Dean kisses his scraped knees.
When he hunts, he fights head on, taking as many hits as he doles out. And so, Dean kisses each and every bruise on his face.
When he shuts the car door, he doesn't pay attention and slams his fingers. And so, Dean kisses his throbbing fingertips.
When he shaves, he does so hastily and cuts himself. And so, Dean kisses the scratches on his neck.
Until one day, when Dean comes home from a trip to the bar with a swollen and bloody lip.
"What happened?" Castiel asked, slightly concerned but mostly bemused as he fetches and icepack from their freezer.
"I got into a fight," Dean muttered, collapsing into a chair.
"Clearly," Cas responded. "But why?"
"Some guy was being a dick to a girl in the bar, so I told him politely to go to hell. And he punched me."
Castiel sat next to Dean at the table, placing the ice pack on his lip. Dean hissed slightly as it made contact with the injury.
"'t hurts," Dean mumbled against the ice pack.
"So be more careful next time," Castiel smiled.
"Make it feel better," Dean whined, picking up on the joke. "Please, Cas."
"What do you want me to do?"
"I don't know," Dean began to smirk. "What makes you feel better when you get hurt?"
Cas smiled, moving the icepack away from Dean's lips and leaning in close, so close their lips were mere centimeters apart.
"I have just the thing."