Reborn as God: The strongest system - Chapter 38 Not For Long

In the year 2220, a radiation source in the Pacific Ocean, tens of thousands of times stronger than a nuclear bomb has begun mutating exposed creatures into horrific monsters thousands of meters long. Mankind’s only hope was nuclear weapons, which only made matters worse. The combination of the natural radiation and nuclear radiation released an incurable and highly infectious virus, turning the 90% of the world’s population into violent zombies in mere weeks.

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.

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

Eight Thousand Years after the Glassing of Earth, Terran Descent Humanity has largely become a post-scarcity society based on consent and enjoying life. With the discovery of another ancient race beyond the “Great Gulf”, events and history collide to draw the Terran Confederacy into war against a hundred million year old empire that has always won and believes it always will. With allies and enemies of multiple species, the Orion Galactic Arm Spur will be wracked by warfare the likes of which have not been seen. Cracked, harried, wounded, and damaged, Terran Descent Humanity willfully throws itself against the universe itself. “The universe hates you and will take away everything you love, laughing while it does so.” - Terran belief.