Excalibur II is the most powerful weapon in the game, although not essential (Steiner, the user of the weapon, can max out his damage without the weapon, and there are no unique abilities associated with the sword). It is obtained by defeating the boss Lich at the end of Memoria in under 12 hours and searching the pillar to the right of the room.
On the PS version of the game, this was considered very challenging, mainly due to unskippable cutscenes and long loading times. On Steam, the challenge is much easier as cutscenes can be skipped, loading is faster, random encounters can be disabled, and the party can be made unbeatable by the use of the built in boosters. This significantly reduces the playtime, allowing the player to clear the game with time to spare.