A New life as a Demon king

Prologue :

My name is Akihiko himura, I'm just a ordinary 15 year old boy who wants to be a weirdly 😅 a Demon king in this god damn world where nobody believes in fantasy, actually people do believe in gods and demons but they only think praying to God will bring luck or prevent them from getting into any bad stuff I don't know why people think that, demons are bad and gods are good, i won't deny that gods are good but I won't accept that demons are bad I just want to prove to the world that demons are not bad, and I don't know why I always believed that God and demons live in the same realm as we do, there is no hell no heaven, welp I just want to become a Demon who has some kind of magic power, who has the strength to level a whole city and the one ig who looks a little intimidating and if possible the one with a Harem 😀