Maybe he turns into a cat because of a misfired spell from a young, inexperienced wizard. And while in cat form, he finds that he can communicate with the magical cats around Hogwarts in a way he couldn't as a human. They tell him secrets about the Forbidden Forest that could help in protecting the school.
In this fanfiction, perhaps a powerful dark magic object turns Harry into a cat. As a cat, Harry's senses are heightened. He can smell danger better and hear things from far away. He might use these new abilities to uncover a plot by Voldemort's followers. For example, he overhears some Death Eaters planning to attack Hogwarts through a hidden entrance that only a cat could access. So he has to find a way to warn his friends while still in cat form and then figure out how to turn back to human to fight against them.
Perhaps all the main characters are transformed into cats at some point. Harry, Hermione, and Ron have to navigate the wizarding world as cats. They might use their cat - like abilities, such as stealth and agility, to solve mysteries and defeat dark wizards. The Hogwarts castle could also have new areas that are only accessible to cats, where they find clues and magical artifacts.
One possible plot twist could be that Kakashi, as a girl, has to deal with different social expectations in the ninja world. For example, she might face more restrictions in combat training because of her new gender. Another could be that she uses her new form to her advantage in undercover missions, fooling enemies who are less likely to suspect a female. Also, there could be a romantic plot twist where a character who previously saw Kakashi as a rival now has different feelings for her as a girl.
One possible plot twist could be that Harry, as James' brother, has a different role in the fight against Voldemort. Maybe he's more of a behind - the - scenes strategist. Since he's in the family earlier, he could have different relationships with the other characters too. For example, his bond with Sirius might be even stronger as they grow up together more closely.
One possible plot twist could be that Kenpachi's rough and battle - hungry nature makes Harry a much more aggressive wizard. Instead of waiting for Voldemort to come to him, Harry might actively seek out dark wizards to fight. Another twist could be in the way magic is taught. Kenpachi, not being from the wizarding world, might introduce Harry to a more physical and unorthodox way of using magic, like using brute force in spellcasting rather than the traditional finesse. Maybe Harry would also develop a more carefree attitude towards the rules of the wizarding world, much like Kenpachi does with the Soul Society's rules.
Well, a possible plot twist could be related to Sasuke's family. Maybe when he turns into a girl, he discovers some long - hidden secrets about his family that were only accessible in this new form. Also, in the ninja world, being a female Sasuke could lead to different political implications. The other villages might view him/her differently and try to use this transformation to their advantage. It could also be a twist if Sasuke, as a girl, has to fight against gender stereotypes within the ninja community.
One possible plot twist could be that Orochimaru turns Naruto into a girl as part of a grand experiment. But Naruto, now a girl, still has his (or rather her) strong will and uses this new form to infiltrate an all - female group that Orochimaru wants to target. This way, Naruto can gather intelligence and thwart Orochimaru's plans from the inside.
One possible plot twist could be that Harry Dresden's magic system clashes with the wizarding world of Harry Potter. For example, Dresden's more rough - and - tumble approach to magic might get him in trouble with the Ministry of Magic. Another could be that Harry Potter, being raised by Dresden, develops a very different personality. He might be more street - smart and less naive compared to his original self. Also, there could be a plot twist where the enemies from Dresden's world start targeting Harry Potter because of his connection to Dresden.
Well, perhaps the nuns are in cahoots with some magical creatures. They could be working with a group of centaurs who have prophesied that Harry must be raised in seclusion among the nuns to gain a certain kind of purity of spirit. Then, when Harry finally enters the wizarding world, he has an aura about him that both attracts and confounds the dark forces. He might also have a special connection to the magical animals due to his time with the nuns, like being able to communicate with them on a deeper level, which would be really useful in his battles against the dark side.
One plot twist could be that Harry's vampiric side gives him an unexpected advantage in fighting Voldemort. Maybe he can use his vampire speed to dodge curses better. Another could be that the wizarding world initially rejects him because of his Dracula heritage, but later realizes they need his unique powers. Also, it could be revealed that Dracula had some connection to the founders of Hogwarts long ago.