It was 100 thousand years ago(in that world's time) when Humans, Elves, and Dwarves lived in prosperity. But then came the invasion from another world, lead by Demon Kind Gundaris(I think was the spelling).
He was the undisputed ruler of his world and controlled his subordinates through fear. He couldn't only kill them, but destroy their very soul. Thus even reincarnation was impossible. Furthermore he had created his own circle of transmigration system (not connected to Rodcorte's system). He lead his army of evil gods and monsters into a world that was ill prepared.
The Gods summoned champions from Earth. More specifically they summoned them from modern times so some had some familiarity with science and technology. Each God choose a champion that they believed fit their own personality. It was a hard battle. The champion Zakkart along the way managed to convince some of the evil gods to switch sides. He was also a proponent in bringing technology(especially weapons) to the world. The champion Bellwood was strongly opposed to this. On Earth he was what one might describe as an eco-terrorist.
Zakkart and 3 other champions where killed by a surprise attack at their lab, and their souls destroyed. Zakkart later was revived(minus a soul) as an undead champion by the Goddess Vida. The war was eventually won, but barely so. The population of the world was reduced to almost nothing. Many gods had been destroyed and the burden of managing the world left to fewer gods. Gundaris could not be totally destroyed but his body was torn apart and individually sealed. Many evil Gods remained scattered about. But that wasn't the end of their troubles.
The remaining great gods disagreed upon the best method to restore their world. Vida bred with various races, evil gods, great beasts, and even the undead champion Zakkart to create new races. Alda was strongly opposed to this. He and the Champion Bellwood where also opposed to every bit of knowledge brought from Earth, and wanted to destroy it all. Alda so the world could develop its own path, and Bellwood because he's an anti-technology zealot. But the breaking point happened when Vida created her own transmigration system modeled after the one Gundaris had created. A civil war among the remaining gods broke out. The evil gods which Zakkart has recruited sided with Vida.
Ultimately Zakkart fell once again and Alda's faction emerged victorious. Although gods normally cannot be totally killed, they can be greatly weakened. Vida was left in a terrible state and hasn't been able to revive even 100,000 years later. She experiences only brief moments of consciousness.
To those who follow Alda's religion (the dominant one), those members of Vida's races are evil that must be destroyed. Although some races more than others(some are classified as monsters). Mortals are not told of transmigration. But the monsters belong to Gundaris's system, Vida's races to her system, and the original races to the system Rodcorte built. Van's parents are a Dark Elf and a Vampire(both Vida's races). Why was he not born a human, dwarf, or elf? That's a future spoiler there.