Not sure how many people on Crunchyroll are also rpg gamers, but I recently got involved with the Dungeon Master's Guild, which allows people to publish d20 material under the Open Game License (OGL).
I've always thought that d20 works well not only for heroic medieval fantasy but for pretty much any genre. The newest edition is a nice balance of streamlined rules and enough detail so that you can get some very unique characters, adventures, etc.
I've written two e-books that provide 5th edition D&D write-ups for firearms. Each e-book has about 200 firearms and other weapons (grenades, missiles, modern blade weapons like machetes and chain saws, etc.)
Being a total geek for anime, I made sure that as many weapons that show up in various anime series and movies were featured in one or the other book. Yes, we're talking about Yoshika Miyafuji's Type 99-1 automatic cannon and Rally's CZ 75 and Sousuke's Glock 26 and...well...a bunch of others. Everything you would need for an anime-flavored d20 campaign set in a world of swashbuckling pirates and musketeers, Old West gunslingers, Steampunk heroes, noir and cliffhanger detectives and monster hunters, modern and Cold War cops and mercenaries and government agents, and probably anything else you can think up. Revolvers, automatic pistols, shotguns, rifles, machine guns. They're all here.
Here are the links...
Please check them out!