chapter 119 - The Beginning Of The Void Century
It begin in the year 493 AD.
The corrupted Mana that the Demon who had a contract with Nero before, fills up the Entire Earth.
From the beginning, The Original Mana has been Sealed for Thousands Of Years, and Because of That, the Humans in the past couldn't use Mana.
After being sealed, the Original Mana which remains on Earth was very little and cannot increase and can only decrease.
And The Mana that spread from the year when Nero asked the devil to be able to use magic until 493 AD is Pure Mana From Hell the "Demonic Manha".
It just needs over 400 years for it to happen, made worse by the small number of Magicians who can manage Mana, That's where 'Fate' begins to shift from its proper path.
In that year (493) Because The Demonic Mana on the Earth was it's already very 'thick', The Demon, the one who makes a Contract with Nero Back to Earth from where he opened a Passage For The Demonic Mana to come to Earth.