Realist Maou Niyoru Seiiki Naki Isekai Kaikaku manga summary:

In a dilapidated castle, Astaroth awoke as a Demon King.
With his ‘wisdom from his past life,’ he would rule over his lands as a thorough ‘realist.’

“Demon King, why are you attacking the level 1 Heroes?”
“Defeat them before they become stronger. That is called strategy.”

“Demon King, why are you sending fake money to the enemy country?”
“To bring chaos to their economy so they will self-destruct.”

“The werewolf troops have attacked. Should we use silver bullets?”
“Not bullets, shoot them with canons.”

And like that, Astaroth ‘reformed’ the old tendencies.
He became a lord who was loved by the people and his subordinates, and he would go on to be called the most powerful Demon King in history.