He might start with the basics at home. Since he has his own experiences at Hogwarts, he can teach her things like the levitation charm. He could use simple objects around the house to demonstrate magic.
Harry would probably also introduce her to books on magic. He could take her to the local wizarding library if there is one, or he might have a collection of books himself. He would encourage her to study and practice the spells she reads about.
He might use magic to make things easier. For instance, he could use spells to cook food and clean up while taking care of his sister. Also, he'd probably rely on his friends a lot. Hermione could help with her studies, and Ron could be there for some comic relief and support.
He would become more responsible. He has to take care of another person now, so he can't be as reckless as he sometimes was. For example, he'd think twice before running into danger because he has his sister to consider.
Well, perhaps in the fanfiction, Harry's little sister has some unique magical ability that attracts unwanted attention. Harry then has to raise her while constantly fending off those who would use her for their own purposes. He would have to balance being a brother and a protector, making sure she grows up happy and safe in a rather dangerous magical environment. He might also introduce her to his friends at Hogwarts for support and guidance as she gets older.
One possibility is that Harry discovers a long - lost sister and takes on the role of a protector. He might teach her magic in secret, away from the prying eyes of the wizarding world authorities. Maybe they live in a hidden cottage and he passes on the skills he learned at Hogwarts to her.
One way Harry Potter could protect his sister in fanfiction is through his fame and influence. People in the wizarding world respect and fear Harry. He could use this to his advantage. If anyone tried to harm his sister, he could make it clear that there would be serious consequences. Also, he might have some special magical artifacts that he could use to protect her. For instance, the invisibility cloak could be used to hide her when needed. Harry's connection with powerful wizards like Dumbledore could also play a role. He could ask for help from them if the situation demanded it.
In the beginning, Delphini would likely be confused and maybe even a bit hostile towards Harry. However, Harry would be persistent in his care for her. He'd tell her stories about his own struggles against Voldemort. As time passes, she begins to understand that Harry is different from what she might have expected. Their relationship grows as they share experiences like going to Diagon Alley together, and Delphini starts to look up to Harry as a role model.
In some fanfictions, it could be through intense emotional experiences. For example, when he faces a great loss or discovers a deep truth about his family, it triggers something within him and unblocks his magic.
In this fanfiction, Naruto's ninja skills could play a role in his sister's protection. He might teach her basic self - defense moves early on. Also, his friends in the village could become like aunts and uncles to his sister, providing different kinds of support and influence. For instance, Sakura could teach her some medical knowledge.
In some Christian Harry Potter fanfictions, magic is seen as a gift from God, much like talents in the real world. It's used for good and is considered a part of the world that God has created. The characters are then tasked with using this magic in a moral way, similar to how people in the real world are supposed to use their abilities for the betterment of others.
Harry would probably be more empathetic towards non - human magical creatures. The Mosasaurus is so different from the usual magical creatures he encounters at Hogwarts. He would understand the needs and feelings of these large and perhaps misunderstood creatures better, which could change his approach to dealing with all magical creatures in general.