Mokuba Kaiba, younger brother to world famous Seto Kaiba, and master of Capsule Monsters. After Atem returns to the spirit world, his life returns to how it was before, rather calm and quiet. However, he is attacked in the early hours of his thirteenth birthday by a soul-sucking demon, and dragged to another world.
Once there, Mokuba discovers that there is no going back, and that he must complete five trials to prove himself to this strange, new world, and to keep him from getting killed, locked up, or ultimately losing his mind. Needed to defeat the very power that brought him here, will Mokuba prove himself to the creatures of this land? Or will he slowly descend to madness?

Disclaimer: Nyx belongs to Pen-Stroke