Event Ancient Period

Not much is known about that timeframe and what really occurred. It could be anything from two to ten decades ago.

Before most recorded history, the Demons of the Dark World and Humans of the Human World were in conflict. Blood of the two were mixing and resulted in the first Taimanin Clans, which were able to fight demons on equal footing.

To avoid the escalating conflict, both sides established the unspoken rule of "non-interference" or "non-aggression".

The rule kept most humans in the dark about the demons and would punish those that actively seeked out powers of the demonic realm, as well as those demons that tried to gain influence in the human world. On an individual level people seem to be allowed to cross the worlds as long as they keeped a low profile and would not cause serious trouble.

The Taimanin and groups like them became the guardians of that rule, protecting the sensible balance of power. However, in the modern and near future world, this rule has been broken by humans and criminal groupse that seek out the technologies and magic of the Dark World. This also resulted in more demons moving into the human world, specially around the time of the Peninsula Conflict.

Trivia

 * The rule of "non-interference" or "non-aggression" is mentioned in almost every Taimanin game, as part of the introduction.
 * The rule "may" also explain why the Dark World is far less high tech, as they actively are not allowed to use technology of the other side.
 * As ancient Demon Gates exist especially around Japan and Taimanin remained local. It could be that the timeframe was at least around the Jōmon period (13,000 BC). The oldest characters mentioned to be connected to the ruling classes of the demon world are around 10000 years, so it would not be absurd of a timeframe.