General terms:
* Conflict: This is the most general term, encompassing any sort of opposition or clash.
* Antagonism: This term emphasizes the hostility or opposition between the characters.
* Confrontation: This term implies a direct and often physical clash between the characters.
* Clash: This term is similar to confrontation, but can also be used for a less physical and more ideological clash.
* Showdown: This term implies a final and decisive confrontation.
More specific terms:
* Battle: This term is used for a physical fight between characters.
* Duel: This term is used for a formal, prearranged fight, usually with weapons.
* Dispute: This term implies a disagreement or argument between characters.
* Rivalry: This term implies a long-standing competition between characters.
* Feud: This term implies a long-standing and bitter rivalry between characters or families.
The most appropriate term to use will depend on the specific context and the nature of the struggle.