I'm not a modder, so I can't even hope to begin to do anything like this, but I've had this idea kidking around in my head for a while. There's this author, Fred Saberhagen, some of you may know of him, or maybe not. He wrote this series "The Books of Swords", about a collection of ancient and powerful weapons.
Most of these would only be worth anything on a server, and some may or may not be possible, but here's the basics if anyone wants to try it.
If all you are wanting to do is add the swords to the game (craftable) It might (emphasis on 'might') be possible to do so via datapacks, similar to resource packs, without having to make an actual mod (ala Forge, etc). This is assuming you are running the latest version of Minecraft (1.13).