Lucifer's Descendant System - Chapter 2: Blessed

A side story series featuring the girls of Kyoukai Senjou no Horizon.

The prosperity is about to come to an end, and the poor boy quietly rises.

Traveling across time and space, seek the leader of the world.

- Description from novelbuddy

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.

In the eyes of outsiders, Yan Ruxu’s conditions are extremely good: good looks, high education, a high salary, and a high position, but there is a fatal flaw: she is divorced, with a three-year-old child. Yan Ruxu didn’t care what others thought of her, she just wanted to raise her son well and live her own life.

- Description from Novelupdates