Really, that's just how legends work in general. It's not uncommon for one Heroic Spirit to be the derivative of an older one.
(Link) That Master Sword's practically identical in concept to a sword we have back home. Excalibur, the Sword of Promised Victory - a divine blade tempered by beings from beyond.
(Link) It's interesting. Despite our completely different Human Orders, stuff like that persists. Hell, maybe a "sword of promised victory" is a necessary insurance all worlds need to survive.
(Stevo) Eeeeyup. I mean, I lucked out by being from Japan at its most isolationist. Cause otherwise I'd be flagged as a weaker derivative of the Tyrfing dwarves. I'm better than them!
Okay, yeah, that makes sense. Your sword's tied to that soul, so it's like your Noble Phantasm, your legendary weapon.
Excalibur, though, is a bit different. It's kept by the Lady of the Lake, typically only lent to a hero in case the rest of the planet's defenses fall. But nothing like that's happened to us yet, so we only know one wielder. One who got lent the weapon when his own holy sword broke.
(Stevo) 161?

He blinks and his back straightens. "Is the 'sword in a stone' legend a thing in your world too?"
dead devotion