I’ll Be the Male Leads Sister-in-Law - Chapter 509

Going against the heavens, Tuoba Ye reincarnated. Body concealing Divine Root, hands holding Divine Talisman, possessing previous life’s experiences, from childhood, began cultivating the most difficult body refining method: Mythical Nine Transformations.

- Description from Novelupdates

Ye Feng was transported to a cultivation world, but unfortunately had no hope of cultivating immortality and could only live as an ordinary mortal. He only wished to live a peaceful life.Yet he didn’t know—The dog he adopted, because it ate his food, became a legendary demon king.The kitchen knife he casually forged became a peerless divine weapon, causing numerous experts to fight desperately for it.The young disciple he took in became an immortal lord that led an era, due to cultivating the techniques Ye Feng taught him.Even the skeletons he looked down on the most were ominous demon kings that suppressed countless worlds.Many years later, looking at the void shattered with a punch, Ye Feng murmured to himself: It turns out the peerless kings were myself all along…

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.