PandoraHearts, Vol. 24 - manga (PandoraHearts, 24)

Someone once said that all they would find there was darkness that swallowed everything whole. But that never meant that light was nowhere to be found--
They finally arrive at an answer to the question of how to save their world. It is the product of many months, even years. Cruel yet kind, it is a simple formula. Now, led on by the cogs of destiny, it spells the end of but one story...as if it were no more than a ridiculous fairy tale.