I love the whole concept of getting the Hero blade or whatever: You get the most powerful sword in the game AFTER you beat all of the most powerful enemies, so that you can use it to defeat all the enemies in the game that you are already infinitely more powerful than.
It's almost as bad as the "spend 5 hours dodging 200 blots of lightning to get a weapon for a character who you never attack with" in FFX.
Defeating enemies with millions of hit points is it's own reward, I guess.
The Mythril Sword is the lowest attack power sword in the game. Vaan has it equipped initially when you start a new game. It can't be obtained any other way than picking up Omega's loot, yielding a maximum of 2 Mythril Swords possible to have in your inventory. For completionists like me, it's nice to know you can get another one.