One scenario could be in the Hogwarts corridors. Maybe some Slytherins are taunting Harry about being a half - blood. In the fanfiction, Harry decides he's had enough. He stands up straight, looks them in the eye, and firmly tells them that his blood status doesn't define him. He uses his skills in magic, like a well - executed non - verbal spell, to show he's not to be trifled with.
Perhaps at a wizarding event outside of Hogwarts. There are pure - blood wizards there who look down on Harry. In this fanfiction situation, Harry stands up for himself by speaking out against the old - fashioned pure - blood ideology. He might give a passionate speech about how all wizards, regardless of blood, should be treated equally. And he could back it up with examples of his own heroic deeds that were not based on blood but on his character and courage.
One possible scenario could be in a potions class. Snape might be unfairly criticizing Harry's work as usual, but this time Harry decides he's had enough. He stands up, looks Snape in the eye, and calmly but firmly defends his potion - making process, explaining how he followed the instructions correctly. This could shock Snape into silence for a moment.
One great 'Harry Potter stands up for himself' fanfiction is 'The Power Within'. In this story, Harry decides he's had enough of being pushed around by the Ministry and starts to take matters into his own hands. He uses his knowledge of magic in unexpected ways to fight against the unjust rules. Another is 'Harry's Rebellion' where he rebels against Snape's unfair treatment in Potions class and shows his true skills and confidence.
I would recommend 'Harry's Solitary Stand'. In this fanfiction, Harry finds himself isolated from his friends due to a misunderstanding. Instead of waiting for them to come around, he stands up for himself and his actions. He embarks on a solo adventure where he discovers new aspects of his magic and his own strength. It's a really interesting read as it shows Harry's growth outside of his usual support network.
Ron and Hermione are the most likely. They've always been by Harry's side in the original series. In the fanfiction, when Harry stands up for himself, they would surely be there. Ron might use his sense of humor to diffuse the situation if it gets too tense, while Hermione would back Harry up with her vast knowledge of wizarding laws and rights.
In these fanfictions, Harry's character often shows great growth. Standing up to Snape means he's overcoming his fear and asserting himself. It could be a sign of his maturing confidence, no longer being intimidated by Snape's harsh exterior. This also might lead to a different dynamic in their relationship, perhaps towards mutual respect as Snape may start to see Harry in a new light.
One scenario could be in a fanfic where Harry Potter reveals himself as a powerful wizard to a group of muggles who are being threatened by dark magic. He steps in, uses his magic openly, and they are both amazed and terrified. Another could be in a school setting within the wizarding world where he reveals a new, secret power he has to his friends to help them in a dangerous situation.
One scenario could be when Molly tries to interfere in Hermione's relationship with Ron. Hermione might stand up and say that she and Ron will figure things out on their own terms, not according to Molly's old - fashioned ideas. For example, if Molly tries to push for a quick wedding, Hermione could firmly state that they are focused on their careers and personal growth first.
In some fanfictions, Harry might use his magic skills in a creative way to outwit bullies. For example, he could use a charm to make the bully's wand malfunction when they try to attack him. This shows his intelligence and ability to stand up for himself and others without using excessive force.
One reason could be a difference in ideology. Harry might have come to believe that Dumbledore's methods, like keeping secrets from him, are not in the best interest of the wizarding world. For example, Dumbledore withheld information about Harry's connection to Voldemort which put Harry in more danger at times. Harry could stand up to him to demand more transparency.
One possible fanfiction could be where Jon Snow stands up to the Night King directly. He might use his skills and knowledge of the enemy to taunt the Night King, saying that he will never succeed in his dark plans. This shows his courage and determination to protect the realm.