Dai Nana Maouji Jilbagias no Maou Keikoku-ki

Alexandre, a hero whose hometown was destroyed by the demon tribe, confronts the Demon King, but get helplessly killed. However, when Alexandre wakes up, he is reborn as the son of the Demon King who killed him, the 7th Demon Prince Jilbagias. In order to strike back at the Demon King, he disguised his true identity and acted as an ideal Demon Prince, which meant acting as a cruel Demon and laying hands on even innocent people…. This is the story of a false Demon Prince who destroys a nation.