Owari no Chronicle - Volume 13, Chapter 38: City of Destruction

After she had transmigrated into the body of an abandoned wife of a little marquis in Ancient China, Su Nuan Nuan, a modern-day food lover was delighted!

She can finally achieve her dream of not caring about the outside world and focus on what she loves best — eating!

But the good times did not last long.

Her husband was curious about these new and exciting dishes, and threw her back into the inner palace.

Then… all hell broke loose!

- Description from Novelupdates

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.

Rainer, an amateur arcanist and college student, sought to create a new spell far surpassing the magic of the few he inherited from his grandfather. Yet the interference of an unknown event during the casting of his spell led him to be thrown through space and time.

Once an imperial princess, now reborn among the lowest of s*aves of the nobility.