Board Thread:Episode Discussion/@comment-14138255-20170101170328/@comment-14138255-20170104210947

Blake in general is just exasperated at Sun for tagging along with her on what was supposed to be pretty much a quiet sabbatical to clear her head. Her slapping him is for comedic effect. It doesn't help that Sun barged in as she was sharing very raw feelings with her father and Sun interrupted them. And he's been rather in your face in everything too (Blake hasn't had many oppurtunities to smile in Sun's presence, had she not been glum anyway).

Sun's biggest contributions are much more subtle too, only truly heartwarming in hindsight. Had he not stowed-away, the ship Blake was on would probably have sunk (or sustained massive damage). And had he not convinced Blake to knock on the door when she did, she might not have or waited a long time (after Fennec and Corsac have made their report, which she wouldn't have been there for). But again, it's only 20/20 in hindsight.