The Dark Light is an Iron Master term referring to electricity. According to the Iron Masters, in the World Before the people of all the world but Nippon in particular became enslaved to the Dark Light. Their dependence on its power for entertainment, transport, the preservation of food and other functions eroded their spirits, in particular the path of honour and obligation known as bushido which had been favoured by their ancestors. The great god Amaterasu-Omikami, furious with his people's decadence, destroyed the world by hurling the sun into the sea, creating a fireball that incinerated the islands of Nippon and even burned the sacred slopes of Mount Fuji.
The only people to survive were those at sea on great floating cities and islands, which in seven great migrations eventually found their way to the eastern seaboard of North America, where they founded Ne-Issan in remembrance of lost Nippon. The Iron Masters vowed never to be seduced by the power of the Dark Light again, and banned its use and all attempts to reinvent it.
During the last century, the family of Yama-Shita pushed for the embracing of technological progress and was permitted to develop steam technology and gunpowder-based weaponry. However, the edict on the Dark Light remained in force. The Yama-Shita and their allies eventually concluded that they needed to re-discover the power of the Dark Light if they were to stand any credible chance of winning the inevitable conflict between themselves and the Amtrak Federation, who had no compunction about the use of electricity and thus had developed a vastly superior military force. The Toh-Yota Shogunate remained firmly opposed to this. However, the eventual discovery that forces loyal to the Toh-Yota had been hypocritically using Dark Light-powered surveillance devices whilst voicing their opposition to its use was a key factor in triggering the Second Ne-Issan Civil War in 2992.