The Ever Cruel Kingdom by Rin Chupeco

After a treacherous journey and a life-shattering meeting with a twin neither knew they had, Haidee and Odessa expected to emerge from the Great Abyss to a world set right. But though the planet is turning once again, the creatures of the abyss will not rest until they have tasted another goddess’s sacrifice.

To break the cycle, Haidee and Odessa need answers that lie beyond the seven gates of the underworld, within the Cruel Kingdom itself. The shadows of the underworld may hunger to tear them apart, but these two sisters are determined to heal their world—together.