Perhaps Hermione discovers that the Order has been using unethical means and she decides to take revenge. She might gather evidence against them and then publicly expose them. This would not only be revenge but also a way to set things right. She could use her knowledge of magic and her vast network of friends to make sure the truth gets out, causing the Order to face the consequences of their actions.
She might get revenge because she felt the Order made a decision that put her or her friends in danger. For example, if they sent Harry on a dangerous mission without proper support, Hermione could plan some elaborate scheme to teach them a lesson. Maybe she'd use her intelligence to expose some of their secrets or weaknesses.
Harry and Ron could be her obvious allies. They've been through so much together, and if Hermione has a reason to get revenge on the Order, they'd likely stand by her side. They trust her judgment and would be willing to help her out.
Perhaps Harry finds out that the Order has made a deal with someone he doesn't trust. In his revenge, he could expose this deal to the wizarding community. He'd use his influence as the Boy Who Lived to make sure the public knows. He might gather evidence and present it in a very public way, like during a big wizarding event. This would not only embarrass the Order but also make them lose the trust of many wizards and witches who previously supported them.
Maybe Ron accidentally ruins Hermione's important experiment in the wizarding lab. In the fanfiction, Hermione could get revenge by getting all their mutual friends to side with her in an argument. She could present all the facts about how Ron's carelessness has cost her time and effort, making Ron feel isolated and guilty.
Well, maybe Boruto's family or friends are hurt by a powerful enemy. So he decides to train hard and seek revenge. He might travel to different places to learn new jutsu and gather allies along the way.
It could be about Sheldon getting back at someone who wronged him in the series. Maybe it's Leonard who ate his last slice of pizza without permission, so Sheldon devises an elaborate plan to make Leonard's life a little chaotic for a while.
Well, it could be about Issei seeking revenge on those who wronged him in the past. Maybe someone bullied him or betrayed his trust, and now he's out for payback. He might use his unique skills or powers to get even.
Obviously, Harry would be the central character. He's the one seeking revenge. Hermione would also likely be involved. She might be torn between her loyalty to Harry and her belief in the Order. If she sides with Harry, she could use her intelligence to help him in his revenge plot, like coming up with elaborate plans to outwit the Order. Ron could also play a significant role. He might initially be against Harry's idea of revenge but then slowly come around as he realizes Harry's reasons.
Maybe Ginny did something that Harry thought was a betrayal, like siding with someone against him in a wizarding conflict. So Harry decides to play some harmless pranks on her to get revenge. For example, he might use magic to make her quill write silly things during a class.
Maybe Harry uses magic to make their house a mess. He could turn Dudley's room into a pigsty or make Aunt Petunia's precious china float and then smash. It's his way of getting back at all the years of mistreatment.
Well, it could be that Rumple discovers some past wrong Dumbledore did to him or his kind. Maybe Dumbledore once meddled in Rumple's magical affairs and now Rumple wants to make him pay. He could start by using his unique magic to create chaos in Hogwarts, like making the staircases go haywire or the portraits misbehave.