Book of Ember: the Last Dragonborn

Orcs were not born in this world. Thousands of years ago, the "War of Ember Abyss" broke out between humans and dragons. The dragons retreated into the abyss and cursed humans before they died - twisting humans into half-human, half-beast "orcs". The curse of dragon blood flows in each orc's body. The more powerful the orcs are, the closer they are to being completely transformed into dragons and losing their minds. Those beings who are completely transformed into dragons are called "embers of the abyss" and are monsters abandoned by the world. Nowadays, humans have long been extinct. The orcs have established a new civilization, but they are always burdened with the fate of the "cursed bloodline". Every hundred years, the "Gate to the Abyss" will open. The orcs must sacrifice their strongest warriors and seal the door with flesh and blood, otherwise the dragons will come back.