There are two extra side stories you can unlock to get some background information on the game's plot.

Story	How to unlock
Alyssa's Story	Place the silver ring (obtained from the vent access in the Cold Sleep Chamber) and place it on Alex's desk (Crew Quarters 6).
Space Leech's Story	Have a Aero Porter, Liberation Maiden or Crimson Shroud save file, finish the game and access Linked Content.