"Alone in the Darkening Depths"
Shadow Nighthunter's fear is losing what little light she has left and becoming a slave to the dark side. Losing her family and being left alone in the world would be the final blow, and it's a constant fear she fights to overcome. For a Sith who holds to a spark of light to keep her from falling to corruption, her life and freedom depends on making sure such doesn't come to pass.

I want to add that when I used the edited brush at first, it looked like fading rays of light seeping into the depths of the ocean. Shadow losing hold of that light would be like falling deeper into the depths of the dark side and the darkness of her soul as the light fades away.