I’m still looking at Irish Myth, but this sword or at least its name got around a bit appearing in Irish, Welsh and English myth. First to Ireland; it appears as the weapon Fergus mac Róich a man who really couldn’t keep it in his pants and had the sword taken from him for sleeping with the wife of Ailill mac Máta (king of the Connachta).
I couldn’t find much about the weapon in Welsh myth but I know it’s there; it bears the same name and many of the same abilities. Which are the ability to cleave the tops off of hills and cut light causing a rainbow to trail each swing of the blade. In both of these incarnations the blade is said to have been a two handed great sword; but in its third it appears as a bastard sword.
This third incarnation being as Excalibur the sword wielded by King Arthur, which i guess really makes it French as the Arthurian legends are derived from French legends.
In Popular Culture
As with our last weapon, this one appears in the Final Fantasy series of games. Most famously as the Celestial Weapon of Tidus in Final Fantasy X. As seen in the beautiful artwork above.
It also appears in Guild Wars 2, as a thorn from the Pale Tree gifted to the Sylvari Riannoc so they could kill Mazdak the Accursed. Those of you who have played Sylvari may have wielded the weapon during your personal story.
In Your Game
Weapon (Greatsword), legendary (requires attunement)
You gain a +3 to attack and damage rolls made with this weapon. This weapon can cut the very light you see, while holding this weapon and not moving you gain advantage on Stealth checks, as light bends around the blade and you. With one swing of this weapon you can remove all difficult terrain within 5 feet of you.
What weapons would you like to know more about?