I Became the Little Demon in Leading Role's Family - Chapter 645 - 655 Because You’re Too Stupid, I Can’t See

A struggling businessman on the verge of bankruptcy finds himself drunk one night, only to wake up in the past—specifically, in 1943 London, amidst the chaos of World War II.This is an era of both immense danger and unprecedented opportunity. It is a time when the British Empire, once the unrivaled superpower where the sun never set, is finally witnessing the dusk of its dominion. Meanwhile, the United States is rising to claim the mantle of global leadership, reshaping the world's balance of power.This is the era where everything begins—where old rulers step down and new powers rise to take their place. This is the era where Pierre finds himself, an era filled with the kind of opportunity he never had before. A small, precious chance to rise, to become a giant, to seize the throne of power, to become a ruler, a world hegemon.

If the gods no longer bestow their mercy, then let us kindle bonfires, carry great swords, become skeletons, or heroes of legend.

In the night, cook wine with the master and discuss the way of heaven and earth!

In the snow, Yu Jian chased the tide of Guangling River!

- 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.