When given the choice to keep the Sword of Aeons you have the choice of throwing it away (this first choice denies you the weapon permanently) and remaining good or stabbing your only sister to death (this second choice is considered evil in most cultures) and keep the sword as a memento of your adventuring career. Instead, you can duplicate the Sword of Aeons (a third choice perferred by game rapists) by doing the following:
Save your game at the Heroes' Guild before fighting Jack of Blades. Go ahead and defeat Jack of Blades afterwards and when you win, don't make a choice about the Sword of Aeons. Instead, do a "hero save" then opt to reload your "world save". You will discover to your sick delight that the Sword of Aeons is in your inventory but you'll be right in front of Jack of Blades. Go and whack him again and you'll gain another Sword of Aeons.
If you're greedy and want some money, do the "hero save" again and reload the "world save" as many times as you desire. When you finally tire of this exploitation, you can make a choice about the Sword of Aeons. Should you decide to remain good, sacrifice one of the Swords of Aeons and keep the rest.