The Simple Life of Killing Demons - Chapter 54Book 12:

The price for saving the world is the right to rule it. After saving a faraway land, Lyn Rivers was cast back to Earth. Wanting the admiration, prestige, and glory of saving that realm, she forced her way back. But she was forgotten, and someone else claimed credit for her deeds. Now, with the power of a deity of destruction, she desires nothing more than to claim her place in history. To do that she will conquer dungeons, make alliances, destroy kingdoms, and build an empire. After all, why ruin the world when you can bend it to your will?

The brash Li Chengfeng makes a living through trickery with his clueless but loyal servant, Xiaobao. One day, the love of his life is murdered, making him a suspect, and he meets a demon who suspects he is the reincarnation of a traitorous immortal.

Bai Aoxue, the best mercenary in the 21st century, is accidentally sent back to the Chengxi Dynasty in Great Continent due to an explosion in her mission, and trapped in the first daughter of Prime Minister. After her rebirth, she is set up by her father to marry the 5th prince Jun Yeyan who wears a mask all day long.
In the face of bloodthirsty enemies, discord between brothers, collusion among courtiers and invasion of enemy state, can Bai and Jun resolve the crises? What will happen to their political marriage? How will the fierce battle for the throne end?
With many twists and turns, the book brings you to experience palace revolution, love and hatred thousands of years ago.

- Description from Novelupdates

In the past life, he was an aerodynamic engineer of a well-known company, and in this life, he is a college student of a famous school.

When the two identities are perfectly integrated, what sparks will appear.

His life experience is also slowly uncovering the mystery, whether he can beat the tycoons of this era, and whether he can stand at the peak of world business.

- Description from novelbuddy