Help! The demon King has a Gun!

What would you do if you were suddenly summoned to another world by the demon king, who wanted to make you his successor? That's what happened to Ren Hoshikawa, a gun-loving high school student who finds himself in a world where magic and monsters are real. But this is not a typical fantasy world. The demon king is actually a nice guy who wants to retire, and the heroes who are supposed to save the world are actually evil and destructive. Ren decides to take up the mantle of the demon king, and use his skills and knowledge of firearms and explosives to fight against the corrupted heroes and their armies. Along the way, he will make friends, enemies, and hilarious mistakes, as he tries to adapt to his new role and his new world.