After gaining control of Japan, the Ninja knew his journey isn't finished yet. Not all Shoguns were defeated, but only those which were crucial to that victory. Soon an enemy shogun decided to overthrow the rule of warriors of the shadow. Year after the conquest, these warriors were continuously attacked by men. A civil war expanded through the country. After five years of bloody fight, the quantity of ninja forces come down to about a dozen warriors. These warriors decided to save themselves and their own secrets. They left the homeland and traveled north in their boats. In a month they reached a continent hardly suitable for life, the ice-lands. But a few people were living there, so the travelers decided to settle. They began to build houses in caves, so that the icy wind wouldn't blow into their faces.
One day something entered a cave by digging through its wall. Even the elder ninjas have never seen such strange monsters. They followed the tunnel to inside the earth. On the other side, a very large battle was in progress. People and demons were fighting. Demons surely wanted come to the surface, people tried to prevent this. With help of the ninjas, demons were easily defeated.
When the last demon was killed, a moment of silence emerged. Ice people and ninjas were looking each other carefully, trying to determine whether they're friends of foes. Some of the people refused to ally with the warriors of shadow, and another battle has started.
The inhabitants who've taken side with ninjas decided to fight their xenophobic brothers. They both understood that the fate of underworld will be decided here, in these dungeons. And demons understood that a third force has emerged for battle to control the Arctic!