Rakuin no Monshou - Volume 12, Chapter 7: Iron Mask

Transform into Divine Dragon and dominate the world!
He is the only Divine Dragon in the sea who founded an underwater Dragon Palace.
With Crawfish Soldiers and Crab Generals as his followers, wild sharks and gigantic octopuses as his subordinates, he is the dragon that rules the city.

- Description from Novelupdates

On that fateful day, a voice in the sky told everyone on Earth that the world they called home has just been part of some sort of simulation.

Chen Miao transmigrated to a supernatural world, where everyone had their own profession, such as “Student”, “Fighter”, “Thief”, and so on.After much contemplation, he activated the “Gunslinger” profession.From then on!While the foreign races brandished their claws to invade, and others tirelessly trained their physical fitness and learned skills.Chen Miao silently ventured into secret realms to collect all sorts of materials, crafting Occupation Exclusive weapons like the “Thompson Submachine Gun,” “Falling Blossom Sniper Rifle,” “Inferno Gatling,” “Matrix Sky-Eye Cannon,” and so on....One day, people suddenly noticed that a very unfamiliar Supernatural Occupation had appeared on the city's Combat Power rankings.And in the crowd.Chen Miao, bare-chested under a black suit jacket with sunglasses on and a cigar in his mouth, held two Inferno Gatlings in his hands, looking up slightly at a group of scoundrels in front of him with the corners of his mouth turned up.“Don't wait for me to stuff the gun barrel in your mouth before you admit you were wrong.”

Arthur, a Rich businessman was kidnapped and tortured for months by men his wife hired. After months of this hell, he was given a second chance, a new life in a different world and, of course, Arthur would rather start a new life than stay and continue to be tortured, so he accepted the deal that was proposed by a mysterious individual, but when he finally was reincarnated, Arthur discovered he was a..... parasite?