I honestly don't remember when I last read this, but I'm pretty sure it was over seven years ago and I think I first read it over ten years ago. The author had a number of "Ranma in a different setting" fics, I remember, including one where Ranma was in a post-apocalyptic landscape where he wielded a seemingly rusted-to-uselessness katana that was actually extremely sharp due to magic (he may have also been traveling with a minor priest underling who somehow gained access to a mystical orb that was incredibly sacred to his religion and gave him tremendous powers he barely understood). Anyhow, in this one, he's left Nerima behind (I think it was established that he did start there) and has become a police officer in another city. He still has insane physics-defying martial arts, but is also comfortable with mixing in handguns. The squad he works on is really quirky, although the only characters I distinctly remember was a female officer who had a violent split personality and a mad scientist type who I think was their medic, as well as coming up with custom equipment. Near the end of where I was reading, Ranma had wound up with a gun that borrowed bio-matter from him to shoot bullets of bone and blood (which didn't bother Ranma because of how quickly he healed) and the group had a genetically-modified creature that resembled a Starcraft zergling (I think it ate a few people before the group found it and decided to adopt it as a pet. It might have initially been introduced via a facehugger that kept killing random people off at chapter ends.
The general tenor of the series was fairly silly. A lot of people died, but no one important for the most part. I want to say that one or more chapters was devoted to them taking down a vampire nightclub with them more or less steamrolling that supernatural opposition between Ranma's martial-arts and general superior firepower.