I'm​ not sure how to customize the sword physically for upgrades, but I have a basic idea for modifications that match the armaments. I'm planning to avoid elemental attacks completely and focus exclusively on pure physical damage output.

Jump: Increases the reach of the sword by creating a wave that extends past the blade and follows it.
Attack: Makes the sword much wider and twice as strong. It creates small shock waves on impact with another surface, briefly unbalancing opponents.
Negate: Creates a smaller shield (with the standard Negate properties) attached to Amie's off hand, allowing for sword-and-shield combat rather than defense exclusively.
Evade: Allows the sword to move faster than the human eye can see, allowing for rapid, almost invisible strikes.

I'm not sure about the Evade one, it sounds kind of lame, but what kind of benefit can you give a weapon in regard to dodging/escaping a fight?