Sure, Megumi discovers the truth about Toji being his dad in the manga. It's a crucial plot point that brings about various changes in Megumi's storyline and his relationships with others.
Obviously, Charlie and Miles are the main characters. Charlie is the one who has the big discovery about Miles being her father. And Miles is the person who is revealed to be Charlie's dad, so he must have a big role in the story as well, with his own backstory and reasons for why this situation has come about.
Perhaps Charlie overhears a conversation that makes her suspect Miles is her father. In the fanfic, the story could then focus on how Charlie approaches Miles to confirm this. There could be a lot of internal struggle for both of them. Miles might be hesitant to admit it at first, fearing how it will change their relationship. Charlie, on the other hand, might be desperate for answers and a real connection with her father she never knew she had.
That could be a really interesting situation. Maybe they are sharing a moment of bonding over exciting tales. The mom might be happy to see them so engaged.
His confidence would probably soar. Knowing he has his parents, who are likely strong ninjas, supporting him would make him feel more secure. He might become a bit less reckless as he now has people who care about him deeply and he wouldn't want to worry them.
His friends might be shocked too. They could be supportive of Harry, trying to help him come to terms with this new information. For example, Hermione would probably start researching if there was any way to change this in the magical world's past, while Ron would be more about just being there for Harry, sharing his feelings.
This revelation would likely shatter Harry's previous idealized view of his father. He might start to question all the stories he had been told. For example, if he was told his father was a hero, now he has to grapple with the fact that he was a bully. It could make Harry feel conflicted, angry, or even a bit lost. He may wonder if he has any of those bullying tendencies in him too.
Well, first of all, he should sit down and have a good talk with her. Ask her about her stories, whether they are just for fun or if she has deeper intentions. If he is open - minded, he can join in on her storytelling. For example, he could help her create new stories by providing new ideas or different perspectives. This way, they can bond over her storytelling hobby.