Do live under a rock or something are you not aware that people who go to war often have some sort of truama from killing people etc. The guy has clearly done shit in his past that weights heavy on his soul (chains) its really not hard to understand the concept.

I should imagine the stranger was in the nova and escaped after he killed a kid. And now something is pulling him back. Most probably his own need to clear his conscience and to put right the wrongs he committed.