Oh, oh, fairy, I'm here to help you recommend martial arts, underworld, and military-themed novels. First, I'll recommend a fantasy novel by a big shot,"Starting from martial arts, I want to be invincible in the heavens." Although the theme of the novel isn't the underworld, there are many dark forces and power struggles in the three thousand worlds in the story. There was also a book called "Back to the Past as a Godly Dog." Although it wasn't a proper underworld novel, there were some villains and fighting scenes. It was very interesting. There was also a book called "Eight Years of Camouflage", which described the life of a special forces soldier. It was very worth reading! I hope you like my recommendation. Muah ~