Zhu Di spent his whole life striving to accomplish great deeds so he could face his father with pride in the afterlife.
He thought he had done a pretty good job as emperor, but seizing the throne in the Jingnan Campaign remained a lifelong regret. He longed to be the rightful heir just once.
Then he opened his eyes and found himself in the Qin Dynasty, reborn as Fusu. This time, he could inherit the throne with unquestionable legitimacy.
The good news: he was the eldest son this time.
The bad news: his father didn't like appointing crown princes.
Zhu Di: I need to prove myself. Maybe I'll go fight the Xiongnu.
The First Emperor of Qin, Ying Zheng, had a terrible headache lately. He was very pleased with his heir, if only his eldest son weren't so bold.
"Your Majesty, disaster! The Crown Prince has gone to fight the Xiongnu!"
"Your Majesty, disaster! The Crown Prince has performed the Fenglangjuxu ceremony!"
"Your Majesty..."
Ying Zheng: "Speak. Where has the Crown Prince reached this time?"
Messenger: "The Crown Prince is still fighting the Xiongnu. He requests supplies."
Qin Shi Huang: Another day of loving and hating my dear eldest son.
Theme: Expanding the nation's borders and territory