“Don’t think of the opponent as someone the hero hates. He may be, or he may not be. The opponent is simply the person on the other side. He can be a nicer person than the hero, more moral, or even the hero’s lover or friend.”
– John Truby, Anatomy of Story (p59)
Does there always need to be an opponent?
well, what else is going to be an obstacle to your character reaching his goal and hack away at his need / weakness and so contribute to his emotional / moral growth (or demise) ?