Crown Prince, Please Show Some Restraint

Su Yang transmigrates into the body of the Crown Prince of Shu, only to end up stranded in another country, where he becomes close friends with its princess, close enough for intimate conversations.

Through one little mishap, he helps the princess become empress.

Through another, he ends up with both the whole realm and the empress.

[The dual transmigration is only used to transport goods. The modern-day plot is barely touched on; the story focuses on the ancient world.]

…

Second synopsis:

After the previous dynasty fell, a century of unrest followed, and the realm split into seven small kingdoms.

In the southwest, the people of Shu live in poverty. The Emperor of Shu has no desire to improve the kingdom; instead, he dotes on his concubine, kills his wife, and slaughters his son. The Crown Prince has no choice but to flee.

During his escape, he is forced to hide in an underground cavern to evade danger, but death still awaits him.

Just then, Su Yang, a modern-day couch potato, transmigrates into his body. Strangely, he looks exactly like the Crown Prince…

Many years later.

When Su Yang returns to Shu with the seals of office of six kingdoms hanging from his waist and an army of hundreds of thousands at his back, the Emperor of Shu finally realizes he was wrong.

And not just a little wrong!