Amber Sword - Chapter 47: Act 17 Valkyrie

A nordic romance that burns up coldly!

The world was once at war with 10 alternate worlds. This was known as the Concept War and our world won 60 years ago. All of this was concealed so no normal people are aware of this fact in the current time.

After the death of his grandfather, the high-school student Sayama Mikoto is suddenly summoned by the giant corporation IAI. He learns this world is headed for destruction due to the acceleration of the Minus Concepts. To prevent this, negotiations must be undertaken with the survivors of the other parallel worlds so their 10 concepts can be released.

And so Sayama is caught up in the final battle to clean up after the Concept War which left behind so much enmity.

When the stars all over the sky open a door on the ground, the disorder of the solar terms becomes pollution, which is a disaster for the world.

Season division came into being.

At the flick of the fingers of the Lixia Commander, thunder and punishment fell from the sky!

Tomb-sweeping Day ordered the master to kneel in front of the grave, and my ancestors saved me!

…

- Description from novelbuddy

Seven years ago, after their breakup, he disappeared without a trace.