Is it enough to say the title of this piece is "The sea moon guardian" and not add anything else? Well, I do like adding a story to each piece but it's not written and I'm doubtful it will ever be but here's a bit that wrote for this:
Every one hundred years, a new guardian is chosen to guard the light of the sea, also known as the sea moon. The sea moon gives light to creatures that live at the bottom of the world but it also has healing powers that only a sea guardian can give. This year, Sealia, the 7th daughter of the 7th sea god, has been decreed as the 777th guardian of the sea moon. She is given the 'Book of Light' and the power to heal. In these days, she sleeps and dreams by the side of the sea moon and makes sure no harm comes to it.
For DC Challenge with the theme, aqua. To view other participants take on the theme, go here.