They're on a mission in Japan when Jack finds something that he thinks describes Mac. It's the art of Kintsugi, of fixing broken things with gold, of showing that these things are more beautiful, more precious for having a history that is not- well, unbroken, for lack of a better word.
Jack watches as Mac laughs with a local kid, showing the boy how to play a game his grandfather taught him.
(Would his father have taught him that game, if he had stayed?)
He leans against a tree nearby the boy's parents, and turns to them when they speak. "You must be very proud of your son."
Jack looks at Mac, a bit surprised. He knows he's a good few years older than the nineteen-year-old, but still. Does he really look old enough to be his father?
Jack huffs out a laugh and speaks almost without thinking about his words. "Brother, actually, but yeah. I am proud."
(Later, Jack will realize that it's the first time he's ever called Mac his brother to someone other than his closest friends or Mac himself.)
The kid looks up and catches his eye, his grin lighting up his face. Jack jerks his head towards the car, wordlessly letting Mac know that it's time to leave.
Mac says a few last words to the younger boy and jogs towards Jack.
The two ride back to the airport in silence, but it's a peaceful sort.
(Jack is glad, in a selfish kind of way, that the kid across from him, asleep in the passenger seat, has had such a hard life. It means that he gets to see this young man grow up, gets to watch him mature and flourish in an environment away from his father.
He gets to watch- and be a part of- the gold filling the cracks that the kid's life has left on him.)