The Unseen World - The Demon of Tears. The Unseen World, #3

Sent by Abyzou into the depths of Inferno, Daria enters the Alley of Tears-one of the most ancient and cursed realms of Hell. Her mission is simple: find the Demon of Tears and destroy him. But nothing in that world is what it seems. When Daria finally stands before the broken creature whose tears burn the ground itself, she discovers a truth that was never meant to be known. The Demon of Tears is not just another ruler of the Inferno.
He is the origin of suffering itself. As long as he exists, pain has a beginning-and an end. But if he dies, suffering will no longer be bound by anything. It will become eternal. Abyzou does not want him destroyed to save the world. She wants him destroyed to unleash an endless cycle of torment across every realm. Faced with a choice that could reshape the balance of Hell itself, Daria must decide whether to obey the demon who sent her.
or betray her and risk becoming something far more dangerous. Because if she makes the wrong decision, suffering will never end. And if she makes the right one. she may no longer be human enough to survive it.