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Zig Zagged: The characters are united by a major conflict..until the next battle when they realize they were better off working alone. But then in the next battle they need each other again. Et cetera.
People on the same side are already friends.
Alternately, people who fought together see no change in relationship.
Enforced: "These are the two lead actors, and we need to show how different their personalities are, and how serious the conflict is. So nothing's going to make them work together unless they absolutely have to."
Lampshaded: "Here's where we fight the Mooks and become friends."
Invoked: "Keep them apart until Monday. That's when the Mooks will attack, and that will forge them together."
Exploited: The enemy the two are fighting instructs his minions to keep them apart, because he doesn't want his two greatest enemies teaming up.
Defied: "Just because we fought the Dark Lord together doesn't mean I've forgotten how you refused to pay the library the fines for the overdue books."
Discussed: "Look at all these new recruits snapping at each other. A good battle, now, that usually changes their attitudes pretty fast."
Conversed: "Weren't those two sworn enemies mere minutes ago?! Those Mooks must've knocked some sense into them!"
Deconstructed: They learn each other's faults after the battle and are disillusioned; a fight doesn't show all your relevant traits.