The Dead Sea: Truth's Awakening

You read from the point-of-view of Kairi Aspido, a girl who lives deep under the surface of Murigen Ocean, in the ruins (or city!) of Kendratome.
One day, Kairi and her closest friend meet uninvited visitors from above the surface. They work together to figure out a way to bring those visitors back home, but along the way, Kairi and company run into even bigger problems.

Problems that reveal there is much more beneath the ocean than everyone thinks.