Perhaps in this 'harry fights back fanfic', Harry discovers some new powers or spells that he uses to fight back. He could be tired of being pushed around by Voldemort's followers or other bullies in the magical community, and he uses these newfound abilities to protect himself and his friends. For example, he might learn an ancient spell from a hidden book in the restricted section of the library. This spell gives him an edge in combat and he starts to turn the tables on his adversaries.
Maybe Harry Potter discovers a new dark threat in the fanfiction and has to fight it using his magical skills and the support of his friends. He could be facing a powerful dark wizard who has found a way to break through Hogwarts' defenses.
Perhaps in this fanfic, Harry teams up with some of his Hogwarts friends. They combine their magical knowledge and courage. For example, Hermione could use her research skills to find a weakness of the Daleks, while Ron provides support and loyalty in the fight. And Harry, being the main hero, directly engages with the Daleks using his powerful spells like Expelliarmus but modified to have an effect on the Daleks' technology.
In this fanfic, perhaps the goblins have some sort of vendetta against a particular group that is also a threat to Harry. So they join forces. Harry could learn a great deal from the goblins' different approach to magic. And together they could stage some epic battles, using the goblins' underground tunnels as strategic points for their fight.
Well, it could be that Merlin, with his powerful magic from his own legend, sees Harry as a threat in Slytherin. Maybe he's been influenced by some dark force in the Slytherin common room. And so, he decides to fight Harry. Harry, of course, would use his Gryffindor - like courage and the spells he's learned at Hogwarts to defend himself.
One possible reason could be a misunderstanding. Maybe Harry is led to believe that Dumbledore has been hiding something crucial about his parents' death or Voldemort's return. For example, if Harry discovers some encrypted files in Dumbledore's office that seem to suggest Dumbledore had a prior deal with Voldemort, it could lead to a fight. Another aspect could be related to power. If Harry feels that Dumbledore is being too controlling over his actions and the use of his powers, he might lash out. In the wizarding world, power struggles are not uncommon, and Harry, as a powerful wizard in his own right, might want to assert his independence.
Obviously, Harry Potter himself. He's the main character who is going to fight back.
The fanfiction could start with Harry being magically transported to Kaguya's world. He'd be confused at first but quickly realize he has to fight to survive. Harry's wand would be his main weapon. He might learn some new spells during the fight, perhaps a spell that can nullify Kaguya's ability to freeze time. As the fight progresses, both characters would start to respect each other's power, leading to an unexpected alliance at the end.
In a 'Harry Fights Alone' fanfiction, the plot could involve Harry being betrayed by his friends. Maybe they are put under a spell that makes them turn against him. Harry then has to face the dark forces all by himself. He might have to rely on his own wits and the few spells he has mastered alone. For example, he could be in a situation where he has to battle Voldemort's minions without Ron and Hermione to back him up, and he discovers new powers within himself during this struggle.
One possible plot could be that Hermikne realizes she has always had deeper feelings for Harry. She might start by reminiscing about their past adventures together at Hogwarts. Then, she could try to find ways to reconnect with Harry, perhaps by showing up at places she knows he frequents. She might also use her intelligence to create situations where they are forced to interact and rekindle their friendship which could potentially lead to more.
In a 'ahsoka fights on umbara fanfic', the plot might involve Ahsoka facing off against various foes on Umbara. She could be dealing with the unique challenges of the planet, like its dark and shadowy terrain. Maybe she has to battle against local creatures or enemy forces that are using Umbara's environment to their advantage.