Perhaps in this fanfic, there's a threat to Hogwarts that only Harry and Snape can figure out together. They are forced to work in secrecy because the rest of the wizarding world still believes Snape to be a Death Eater. As they spend more time together, they find they have more in common than they thought. Harry realizes Snape's deep love for the school and his desire to protect it, which in turn makes Harry trust Snape more and more.
One possible plotline could be that Harry discovers Snape's true motives much earlier. Maybe he stumbles upon Snape's memories that show his complex relationship with Harry's mother. This new understanding makes Harry see Snape in a different light. They start to have secret meetings where Snape teaches Harry advanced magic, away from the prying eyes of others at Hogwarts. Their relationship gradually evolves from one of enmity to an unspoken bond.
In this fanfic, it could be that Snape is actually Harry's real - life mentor in disguise. He has been secretly guiding Harry all along, but in a way that makes it seem like he hates him. As Harry starts to suspect something, he begins to follow Snape secretly. Eventually, he confronts Snape, and they start a secret alliance. They then work together to uncover secrets about Harry's family and the Dark Arts that Dumbledore never told Harry.
Another plot could involve Kakashi's relationships. Since she is secretly a girl, her interactions with other characters, like Naruto and Sasuke, might take on a different tone. For example, she might have a more nurturing side that she has been hiding. She could also have a love interest that is initially confused by her masculine facade but later discovers her true self.
One possible plotline could be that they keep their marriage a secret to avoid the chaos it would cause in the wizarding world. They might have some sort of deep understanding that developed over time, which led to their union. Another could be that they got married for some sort of strategic reason, like protecting each other from certain threats.
Well, a plot could be that Snape adopts Harry due to some unforeseen circumstances. For example, Dumbledore in his infinite wisdom decides that Snape is the best person to protect Harry. Snape initially hates the idea but as he spends time with Harry, he starts to see Lily in him, not just in appearance but in his kind heart. This makes Snape more protective. Harry, for his part, is initially scared of Snape but soon realizes that Snape is actually trying to help him grow into a powerful wizard. They start to have a mutual understanding, and Snape helps Harry with his studies and also with dealing with the trauma of his past.
One possible plotline could be that they start to secretly help each other with their studies. For example, Draco might be struggling with a certain type of magic that Harry is good at, like Patronus Charms. In secret, Harry could give Draco some tips. Another could be that they team up to solve a mystery in Hogwarts that no one else is aware of. They might discover a hidden chamber or a secret spellbook together. They would have to keep their friendship a secret because of the rivalry between Gryffindor and Slytherin. Their friendship could also be tested when their respective houses are in competition, but they still find ways to support each other on the sly.
One possible plotline could be that Harry grows up with a very different set of values. Since Lucifer is often associated with rebellion and a certain kind of dark knowledge, Harry might be taught to question authority in a more extreme way than in the original series. He could also have some very unique magical abilities that are influenced by Lucifer's nature, perhaps abilities related to darker forms of magic.
Perhaps there's a plot where Snape is framed for a crime he didn't commit, and Hermione is the only one who believes in his innocence. She sets out to prove his innocence by investigating the real culprit. Along the way, they have to work together, hiding from the Ministry of Magic and other dark forces. Snape starts to see Hermione in a new light, and Hermione gains a deeper understanding of Snape's character and the politics within the wizarding world.
One challenge could be the public perception. In the wizarding world, Snape is often seen as a villain or at least a very unlikable character. So for Harry to be secretly with him, Harry would have to deal with the potential backlash from his friends like Ron and Hermione, who might not understand his new relationship with Snape.
One possible plotline could be that Harry discovers a hidden family connection to the Death Eaters. Maybe his real parents were involved in some dark magic and he starts to explore this side of his heritage, which gradually makes him more sympathetic to the Death Eaters. Another could be that he is tricked by a powerful dark wizard into believing that the Death Eaters' goals are actually good for the wizarding world, so he starts working with them secretly.
One plotline could be that they got married secretly to protect each other. Maybe Snape has some dangerous enemies and Hermione wants to help him, so they tie the knot in secret. Another could be that they fell in love while working on a very complex magical project together and decided to marry without anyone knowing because they feared the reaction of others.
One possible plotline could be that Harry discovers Snape's past and the reasons behind his harsh behavior. For example, Harry might find out about Snape's love for his mother. This new understanding could lead to an initial truce between them. They could start by working together on a difficult potion in the classroom, with Harry being more patient and Snape being less critical. As time passes, they might find themselves sharing their thoughts about the wizarding world's future and realizing they have more in common than they thought.