I just thought of idea of what if a water gun was added to the game and I think when a little too deep with this but if anyone reads this feel free to added on to it.
Water: Zero damage but make people wet and lowers there defend a little.
Bug Vemon: Zero damage but slowly poison enemies' overtime with each shoot.
Cum: Deals big lust damage but does zero damage when use against Meat Parasites and Succubus which just heals them.
Temple Bath Water: Strong against Meat Parasites and Ghosts, Cause be use in some puzzles around the world, but you need to pay the Kitsune every time you need to refill.
Meat Parasite Juice: Slowly drain health and increases lust but you have to fight Meat Parasites for it.
Fairy Dust Water: Deals damage equal to the character Mys stat, can sometime make the enemies distracted.
Breast Milk: Deals lust damage and can be used for you private events with some characters.
Soup?: All do zero damage.
This is actually really interesting, and how effective the weapon is can be determined from senses, because you need to be able to see what your shooting. It'd add an interesting third way of attacking, and with different ways to use it. It might be a little difficult to code, but sounds interesting.
I do agree, it'd be interesting and fun to use, but as someone who's going into game development, it would be a lot of systems to implement. Plus since most attacks are melee range, does that mean you'd do damage, and they hit you back? It's a lot of things to implement, but I do agree it sounds fun, and could be an interesting weapon to use.