Secrets.

Sasuke Uchiha was a very private person, working hard to keep people at arm's length since it was much easier than dealing with their reactions. When his co-worker Naruto finds out about his most closely held secret, they strike a deal to keep it between them.

However, the closer he gets to his loud co-worker, the harder it gets to keep himself hidden and he is forced to deal with the fear of letting someone else in to his quiet as zlittle world.