He finished the slope of the nose and sat back to take a look at his work.
"No, Castiel, the nose is all wrong. You must do it like this," said Michael, taking the charcoal out of his hand and making a smooth parenthesis over Castiel's smudged-out nose. Castiel's hands were already a dark gray from smudging out his mistakes. He preferred this - using charcoal - to the use of pencil, because this way he didn't get eraser shavings all over him. Just his hands were dirty, this way.
"Now you try," said Michael. Castiel accepted the charcoal back from his brother and tried to copy the exact slope of Michael's outline. "Good, Castiel." Michael tore the piece of paper out of the sketchbook that was resting on an easel. "Now, again."
Castiel would have sighed if he had been allowed it. He had been drawing Dean Winchester for days now - or, what counted as days on Earth. Everyone knew of the prophecy that they would be sent into battle to save Dean Winchester, and that one of their garrison would be the one to save him. The prophecy did not specify who it would be, but Michael seemed sure that it would be Castiel. Hence the private lessons. Castiel was required to be able to put Dean Winchester back together, to stitch the very atoms of his being to each other. The lessons were just practice. For with every swipe of charcoal, he wasn't just drawing Dean Winchester. He was memorizing the very existence of Dean Winchester.
Right now, on Earth, Dean was just a four-year-old boy, enraptured by his new baby brother. But time was fluid in Heaven, not at all linear. Castiel had been watching Dean Winchester for some time now. He had seen Dean on his first hunt, his first day of school (and on his last day of school), his first kiss, his first girlfriend. Castiel had seen all of Dean's firsts, and everything in between (his favorite was the night that Dean showed up at Stanford to see his brother after years apart).
With each new mark on the page, Castiel was drawing Dean's life. If he wasn't careful, he could lose himself in his work. Michael had warned him of this. "You mustn't get close to your charge, Castiel, especially if your first charge is to be Dean Winchester. You must maintain a safe distance." And yet, he had thoughts that maybe it wouldn't be so bad to be close to Dean.
With one final sweep of the charcoal, he sat back to better see his work.
"Castiel..." began Michael. He looked at his younger brother. "Well done."