Lord Seiko Chikatilo

"'But you already know who I am, don't you? Does darkness not ring a bell to you anymore? Am I worthless as light itself?'"Lord Seiko Chikatilo is the ultimate antagonist of the series. He is the bringer of darkness and wishes to destroy all things light, and is the ultimate nemesis of the elementals and The Storyteller.

History
Lord Seiko Chikatilo does not have a known family, and named himself.

In the prologue teaser, a meditating Storyteller describes a battle for power at the start of time between light and darkness. Referring to light is referring to The Storyteller, as referring to darkness is referring to Lord Seiko Chikatilo.

As far as The Storyteller describes it, the battle raged on for eons. Eventually, she won, trapping them both in separate portals forever.

Through unknown methods, Seiko then escaped and left The Storyteller panicking - she couldn't prevent him from taking over, so she created the elementals as a result, to battle him and defeat him as she once could not finish.

He is mentioned hundreds of times throughout the history of the earthly elementals. At first, the battle is thought to be a whizz. However, the complete and ultimate underestimation of his elemental power of darkness leads to the deaths of hundreds of elementals.

It is clearly shown that Seiko created an underground bunker for secretive purposes. Eventually, it is made clear that he has been working on the Power Development project, which makes it easier to defeat all the elementals in one blow.

Abilities
Seiko is the elemental of darkness. Naturally, The Storyteller, the creator of the elementals and the elemental of light would be his arch-nemesis. But several of his abilities, such as black holes, can absorb light, rather than vanish from it.

Although generally thought of as a destroyer than a creator, it's true he can do both. He can both create and destroy darkness, and he chooses to create it. You can't just keep chipping away at light, either.