It wasn't unknown to anyone that Castiel and Nathaniel had a deadly rivalry since, well, always. The two always found ways to spite and sabotage each other one way or another, which only fueled the hatred between them as time went by.

It never went further than that, however. Yet one day, Castiel finally got to his breaking point and soon enough those two were about to fight like wild cats. And, of course, now it was your problem to separate them.