Bewitched

As if the world is coming to an end when such creatures called 'giants' appeared to the world of humans to destroy everything but it was said that another creature with pale skin and red eyes which is believed as 'vampires' came to defend the humans from said giants but humans will become livestock in return.

But the pride of humanity never dies thus they created a pact to another creature which is believed as 'demons' and this said demons became weapons for the humans to protect theirselves from two dangerous creatures in this chaotic world.

and Hesaiera witnessed all of this happenings.

[inspired by Owari no Seraph]