Orochimaru is a major villain in the Naruto series. He was once a part of Konoha. He was obsessed with immortality and forbidden jutsu. He defected from the village, performing many cruel experiments on people. He sought to gain new bodies to prolong his life. He was extremely powerful and a master of various snake - related jutsu. He also trained Sasuke for a while, hoping to use Sasuke's body in his immortality plan.
McGregor's unruly behavior and his disrespect towards Khabib. He said things that were completely unacceptable. Khabib, being a proud fighter with strong values, couldn't let those remarks slide. So, he took on McGregor in the fight to set things straight and prove his worth in the MMA world.
Minato might also be a prominent character. As their teacher, he can influence the way Obito and Kakashi interact. In some fan fictions, he could be the one to help them resolve their differences or provide some crucial information about their past that changes their current situation.
There was a girl and a boy in a competition. It was a race. The boy was overconfident and made some taunting remarks towards the girl before the race. This made the girl determined to win. During the race, the boy tried to block the girl's path a few times. The girl, not one to be bullied, elbowed him gently but firmly out of the way. In the end, the girl won and the boy was left fuming. But the girl just walked away with a proud smile on her face.
Once, I saw a wife and a mistress have an argument in a park. The wife found out about the mistress and confronted her. The mistress tried to act tough at first, but the wife was full of anger and rightful indignation. The wife started shouting about how the mistress was ruining her family. In the end, the mistress, feeling ashamed, ran away.
Some fanfictions might explore the emotional aspect of their fight. For example, how their past friendship affects the battle. Maybe Kakashi hesitates to strike a fatal blow because of their shared history.
Naruto would likely win. Godlike Naruto implies he has extraordinary powers. Naruto has strong chakra reserves, and his signature jutsus like Rasengan are extremely powerful. Also, his ability to quickly adapt in battle gives him an edge over Orochimaru.
Jealousy. The wife is jealous of the mistress for stealing her husband's attention and love. And the mistress might be jealous of the wife's legal position in the man's life.
In RWBY fanfiction, the Weiss vs Winter fight can be a display of their different combat styles. Weiss is more about grace and precision with her Glyphs, while Winter, being more experienced, has a more refined and perhaps harsher style. Their fight could also explore their complex relationship as sisters.