I think a mechanic that would integrate well into STARBOUND would be the player being able to court a humanoid NPC, and then eventually marrying them if they "win" them over. Think how Fable II handled this, where child NPCs were also even eventually born from the pairing. Things such as gifts/flowers/etc. could be given to the NPC significant other in order to woo them. A player would also have to choose a "home" for his new family.