Final Fantasy 15 got a new patch on PC yesterday that brought with it official mod tools. Less than a day later, the Steam Workshop is already rife with, among other things, keyblades. Who would have guessed.
Called Mod Organiser, the new set of tools is Square Enix's way of adding official support for mods. It also gives players in-depth instructions on how to add their own preferred nonsense into the game, including new weapons, costumes and, uh, Thomas the Tank Engine apparently.
Currently the mod tools make it possible to replace character models and textures with custom ones (see above), though Square Enix will no doubt expand them in future updates. The easiest thing so far has been adding weapon to the game, and currently you can deck out Prince Noctis in any number of non-canonical, copyright infringing weapons from other games:
Definitely not Kratos' blades.
The Monado from Xenoblade Chronicles.
Cloud's Buster Sword from Final Fantasy 7.
And, uh, Prompto?
It's only a matter of time before beloved characters from other Final Fantasy games start popping up there.
Currently, my favourite mod comes by way of Steam user MIMECH2, who had the opposite idea and decided to take characters out of the game. If you're interested in playing Final Fantasy 15 with Noctis completely missing from the game because he's sort of a whiny arsehole, that's an option now.