The science of the alien era has almost brought mankind to the brink of extinction. In the "final battle" of 3000 years in Bit Calendar, mankind's scientific ability was also ruined, and the plague gnawed away at mankind like a devastation. In order to survive, the remaining humans are trying hard to find the lost civilization and power, and have to go back to the way of life thousands of years ago and start over.
In order to gain power, many people are willing to pay a huge price to enter Eibon, the legendary sanctuary of scientific power, and become mercenaries, although there are too many ulterior secrets and conspiracies behind it all.
Sakland joined that hellish organization just to find the missing part of himself.
And his unfulfilled wishes.