While the people of the sea doesn't share biological bonds the same way the sky dwellers (aka "Human beings") do, Marin still considers Urin to be her little sister. When the ring drops into the sea and Marin decides to head up there and return it, Urin follows her, concerned about what she heard about the sky dwellers. Later, she accidentally (and partially through manipulation) frees one half of the entity known as Sedna.