Great Tang: I'm a Spendthrift, So Why Are You Worried, Li Shimin?

Cheng Chumo transmigrates as Cheng Yaojin's son and binds himself to the Spendthrift System: for every tael of silver he wastes, he gets ten taels' worth of modern supplies. He becomes Chang'an's number-one wastrel, treating beggars to meals, gambling away farmland, and melting weapons down to make iron pots, while Cheng Yaojin chases him around with a belt.

Then the Turks reach the Wei River. In the dead of night, he opens the granary and hauls out three thousand modern repeating crossbows, crushing Jieli Khan's forces in a single night. "Dad, I'm not wasting money. I'm stocking up!"

After the war, he's made a marquis. He starts group-buying grain, flash sales, Tang Dynasty ride-hailing, and a banknote revolution, crashing the great clans' grain prices. When Wei Zheng impeaches him, he does the math right there in court. He's granted a marriage to Princess Yong'an, and the two go from disliking each other to secretly helping him manage the books. Then the truth behind the System is revealed: it's a distress signal from the future Tang Dynasty.

See how the Tang Dynasty's number-one wastrel grows stronger the more he spends, and spends his way into a golden age for the Tang!