In Another World, I Must Defeat the Demon King by Miles English

Don't bring a sword to a gunfight... Unless it has +5 radiant damage.
Henry's life as a valiant defender of the realm is over—stolen away when he is transported to a strange new world. Instead of horses and swords, it has cars, rent, hamburgers, and a gun-toting part-time waitress named Shana. There isn't much use for a white knight atop a fiery steed. or is there?
Thankfully, Henry's ability to level up and unlock powerful new skills hasn't abandoned him. In fact, Shana is starting to level up, too. But there's a catch. Turns out, they've caught the attention of a secret society that's devoted to the very system of power that Henry was raised on. Led by the enigmatic Demon King, they aren't happy about newcomers getting involved in their affairs. Magic, power, experience—the Society wants it all for themselves, and they'll happily kill whoever it takes to keep it that way.
"A fast, fun, and funny new LitRPG adventure series from debut author Miles English that will leave you turning pages well into the morning!" — James A. Hunter, bestselling author of Viridian Gate Online, Rogue Dungeon, Shadowcroft Acadmey , and co-author of Bibliomancer with Dakota Krout