Backstory

On his home planet, everyone shares their feelings and problems openly, as they can all see when someone is feeling badly and one's emotions will effect others around them. However, managed to get trapped far away from his own species and surrounded by those who were blind to his feelings. His species needs that kind of emotional intimacy to survive, they leach off each other subtly in a way that would go nearly unnoticed constantly. Without that consistency he'd need a much more noticeable amount that has a chance of injuring whomever he attacks. (Think of it like platonic Hanahaki Disease without the flowers.) He can't chance hurting his crewmates, so he keeps to himself and takes to the streets, unleashing vampiric vigilante justice on those who he deems worthy in each space port they land in, but sometimes it is difficult to find somebody worthy of the pain his feasting can cause. Worse still is when he learns that he was wrong. Around his crew he is aloof and standoffish, his cynical attitude doesn't help either. If at all possible he avoids direct skin contact with them. Despite all of this, he is a good person. All of this will be eating him up inside.