From the introduction: The Great Blue Sea. A vast ocean that covers most of the world. Hundreds of years ago, it was ruled by the Sea God, beloved of all his subjects. His twin daughters, Uomi and Mikotsu were similarly adored. But he was to fall asleep for an unknown period of time. He chose Uomi to rule in his place, for he thought she was the better ruler. Mikotsu took this decision as a sign that her father loved her sister more than her. Bitterness and rage overtook her, and she formed a rebellion. A sizable chunk of the ocean’s populace thought Mikotsu was a better choice than Uomi, and the two factions split into a great war. Then, through magic and her great power as a godling, Mikotsu created the Sea of Death to turn favor to her own side. It empowered her and her minions, bringing the dead back to life, and poisoned the ocean. The living on her side became undead monstrosities.