Mortal Demon King's Struggle for Hegemony

A mediocre 42-year-old middle-aged uncle was suddenly summoned to a medieval magical world. He was also regarded as the devil king of another world, and he wanted to conquer the world with the female devil who summoned him. But he is just a mortal. Although his body has returned to the age of 18, he has no system or plug-ins. In this world, which can be called the Warring States Period, there are: The demon empire formed under the leadership of seven elector princes; The centralized empire of humanity; An elven republic with the Senate as the oligarch; The United Kingdom where humans and elves marry; The dwarf arms dealer who made a fortune from war; A violent and bloodthirsty orc mercenary group; The centaur tribe known as the "Overlord of the Plains"; As well as werewolf warriors, vampire loan sharks, lizard sailors, magicians association, witch group, church of gods, apostles, sons of gods, other time travelers... As a mortal, how can he survive, rise, and strive for hegemony in this cruel and realistic world, and eventually become the Demon King?