Ragnarok-
Is found in Lunar Subterrane and must defeat Dark Bahamut to get it
Beware of its power this is one mean monster you're facing

Holy Lance-
Is also found in that place now you must face Plague Horror a small flying eyeball creature will cast doom at the entire party Quickly damage the boss and have Kain use Jump on it
Everyone will die as Kain will be in the air use the Phoenix Down on anyone and continue the battle And you will get the Lance

Masamune-
Defeat Ogopogo boss to get this weapon
This boss is similar to Leviathan but even stronger

Murasame-
Defeat the White Dragon to get this weapon
NOTE: Your party will have fatal death if it counters with 'Quake' have Rosa cast Float to your party

And that's all you need to know to get these ultimate weapons from
Onion Swords and other stuff like that coming soon =)